So what do you believe, you previously wrote:
Is the Prophet Muhammad [Peace be upon him] a Prophet only for those people who lived during his life and those people to come untill the day of Judgement or is The Prophet Muhammad [Peace be upon him] a Prophet sent to all Mankind, there is A hadith in Sahih Muslim "Ursil thu ilal khalqi Kaafa" and the many Quran Ayahs that say the Prophet was sent for all Mankind.
So if he was sent to All Mankind, meaning All Humans and All Jinns then that also means he is the Prophet of All Mankind including the other prophets.
So clarify for me, what is your position, was Muhammad, peace be upon him sent to Mankind, before and after his coming, as your words, "So if he was sent to All Mankind, meaning All Humans and All Jinns then that also means he is the Prophet of All Mankind including the other prophets." indicate, or do I follow your position that people did not have to believe and place him in their testimony of faith?
Also you asked if he's a prophet, peace be upon him, for just the people of his lifetime and us or All mankind. It does not need to be an OR question, he is both, in the context given.
Well unless there is a reason for us to believe otherwise why shouldnt we accept that?
All Mankind could mean different things, so, we go to the Tafsir books to find out what it means, this is why I refered you to the Tafsir.
Just us alone in this thread can understand 'All Mankind' to mean different things:
*Mankind from before and now
*Mankind to come till the end of time, i.e. the remaining
For as you have said, it could be All mankind from before Adam.
Or as Grace Seeker has said it could mean all mankind now as he said:
All mankind could mean all those presently living at the time the phrase is spoken, or at whatever time the referred to action takes place.
For instance, if the Prophet had said that all mankind would die in a nuclear holocaust, would mean that all of humanity that previously existed would have to be brought back to life, just so that they could die in the nuclear holocaust. But that at the time of some future nuclear holocaust, all those living at that time would die in it.
So for this reason I asked you to go to the Tafsir.
If you had done so, and openly accepted the Tafsir, you'd see:
Muhammad bin Ka`b said concerning the Ayah:
﴿وَمَآ أَرْسَلْنَـكَ إِلاَّ كَآفَّةً لِّلنَّاسِ﴾
(And We have not sent you except to all mankind) meaning, to all the people. Qatadah said concerning this Ayah, "Allah, may He be exalted, sent Muhammad to both the Arabs and the non-Arabs, so the most honored of them with Allah is the one who is most obedient to Allah.'' In the Two Sahihs it was reported that Jabir, may Allah be pleased with him said, "The Messenger of Allah said:
«أُعْطِيتُ خَمْسًا لَمْ يُعْطَهُنَّ أَحَدٌ مِنَ الْأَنْبِيَاءِ قَبْلِي: نُصِرْتُ بِالرُّعْبِ مَسِيرَةَ شَهْرٍ، وَجُعِلَتْ لِيَ الْأَرْضُ مَسْجِدًا وَطَهُورًا، فَأَيُّمَا رَجُلٍ مِنْ أُمَّتِي أَدْرَكَتْهُ الصَّلَاةُ فَلْيُصَلِّ، وَأُحِلَّتْ لِيَ الْغَنَائِمُ وَلَمْ تَحِلَّ لِأَحَدٍ قَبْلِي، وَأُعْطِيتُ الشَّفَاعَةَ، وَكَانَ النَّبِيُّ يُبْعَثُ إِلَى قَوْمِهِ خَاصَّةً وَبُعِثْتُ إِلَى النَّاسِ عَامَّة»
(I have been given five things which were not given to any of the Prophets before me. I have been aided by fear (the distance of ) a month's journey. The entire earth has been made a Masjid and a means of purification for me, so that when the time for prayer comes, any man of my Ummah should pray. The spoils of war have been made permissible for me, whereas they were not permitted for any before me. I have been given the power of intercession; and the Prophets before me were sent to their own people, but I have been sent to all of mankind.)'' It was also recorded in the Sahih that the Messenger of Allah said:
«بُعِثْتُ إِلَى الْأَسْوَدِ وَالْأَحْمَر»
(I have been sent to the black and the red.) Mujahid said, "This means to the Jinn and to mankind.'' Others said that it meant the Arabs and the non-Arabs. Both meanings are correct.
Extract, Tafsir of Surah 34, heading The Prophet was sent to all of Mankind Allah says to His servant and Messenger Muhammad, I encourage everyone to read it.
Allah says to His Prophet and Messenger Muhammad ,
﴿قُلْ﴾
(Say), O Muhammad,
﴿يَـأَيُّهَا النَّاسُ﴾
(O mankind!), this is directed to mankind red and black, and the Arabs and non-Arabs alike,
﴿إِنِّى رَسُولُ اللَّهِ إِلَيْكُمْ جَمِيعًا﴾
(I am sent to you all as the Messenger of Allah,) This Ayah mentions the Prophet's honor and greatness, for he is the Final Prophet who was sent to all mankind ﴿and the Jinns﴾. Allah said,
﴿قُلِ اللَّهِ شَهِيدٌ بِيْنِى وَبَيْنَكُمْ وَأُوحِىَ إِلَىَّ هَـذَا الْقُرْءَانُ لاٌّنذِرَكُمْ بِهِ وَمَن بَلَغَ﴾
(Say, "Allah is Witness between you and I; this Qur'an has been revealed to me that I may therewith warn you and whomsoever it may reach.'') ﴿6:19﴾,
﴿وَمَن يَكْفُرْ بِهِ مِنَ الاٌّحْزَابِ فَالنَّارُ مَوْعِدُهُ﴾
(but those of the sects that reject it, the Fire will be their promised meeting place)﴿11:17﴾, and,
﴿وَقُلْ لِّلَّذِينَ أُوتُواْ الْكِتَـبَ وَالاٍّمِّيِّينَ ءَأَسْلَمْتُمْ فَإِنْ أَسْلَمُواْ فَقَدِ اهْتَدَواْ وَّإِن تَوَلَّوْاْ فَإِنَّمَا عَلَيْكَ الْبَلَـغُ﴾
(And say to those who were given the Scripture and to the illiterates (Arab pagans): "Do you (also) submit yourselves (to Allah in Islam)'' If they do, they are rightly guided; but if they turn away, your duty is only to convey the Message.) ﴿3:20﴾ There are many other Ayat and more Hadiths than can be counted on this subject. It is also well-known in our religion that the Messenger of Allah was sent to all mankind ﴿and the Jinns﴾. Al-Bukhari recorded that Abu Ad-Darda' said, "Abu Bakr and `Umar had an argument in which Abu Bakr made `Umar angry. So `Umar went away while angry and Abu Bakr followed him asking him to forgive him, but `Umar refused. `Umar shut his door closed in Abu Bakr's face and Abu Bakr went to the Messenger of Allah while we were with him. The Messenger of Allah said,
«أَمَّا صَاحِبُكُمْ هَذَا فَقَدْ غَامَر»
(This fellow of yours (Abu Bakr) has made someone angry! `Umar became sorry for what he did, went to the Prophet and greeted him with the Salam and sat next to him, telling him what had happened. The Messenger of Allah became angry (at `Umar), and realizing that, Abu Bakr said, `O Allah's Messenger! It was me who was unjust.' The Messenger of Allah said,
«هَلْ أَنْتُمْ تَارِكُو لِي صَاحِبِي؟ إِنِّي قُلْتُ: يَا أَيُّهَا النَّاسُ إِنِّي رَسُولُ اللهِ إِلَيْكُمْ جَمِيعًا فَقُلْتُمْ: كَذَبْتَ وَقَالَ أَبُو بَكْرٍ: صَدَقْت»
(Will you leave my Companion (Abu Bakr) alone! I said, `O People! I am the Messenger of Allah to you all,' and you said, `You lie,' but Abu Bakr declared, `You said the truth.')'' Al-Bukhari recorded it. Imam Ahmad recorded that Ibn `Abbas said that the Messenger of Allah said,
«أُعْطِيتُ خَمْسًا لَمْ يُعْطَهُنَّ نَبِيٌّ قَبْلِي وَلَا أَقُولُهُ فَخْرًا بُعِثْتُ إِلَى النَّاسِ كَافَّةً الْأَحْمَرِ وَالْأَسْوَدِ وَنُصِرْتُ بِالرُّعْبِ مَسِيرَةَ شَهْرٍ وَأُحِلَّتْ لِي الْغَنَائِمُ وَلَمْ تَحِلَّ لِأَحَدٍ قَبْلِي وَجُعِلَتْ لِيَ الْأَرْضُ مَسْجِدًا وَطَهُورًا وَأُعْطِيتُ الشَّفَاعَةَ فَأَخَّرْتُهَا لِأُمَّتِي يَوْمَ الْقِيَامَةِ فَهِيَ لِمَنْ لَا يُشْرِكُ بِاللهِ شَيْئًا»
(I have been given five things which were not given to any Prophet before me, and I do not say it out of pride. I was sent to all mankind (their) black and white alike. Allah made me victorious by fright, (by His frightening my enemies) for a distance of one month's journey. The spoils of war are lawful for me, yet it was not lawful for anyone else before me. The earth has been made for me (and for my followers) a place for praying and a thing to perform purification with. I have been given the Shafa'ah (right of intercession), and I saved it for my Ummah on the Day of Resurrection. Therefore, the Shafa'ah will reach those who associate none with Allah in worship.) This Hadith's chain of narration is suitable, but the Two Sahihs did not record it.
Extract of Tafsir Surah 7, heading Muhammad's Message is Universal, I encourage everyone to read it.
So it is clear, we can see, All mankind means, not only to his own people, as the previous prophets and messengers, peace be upon him, rather he was special, he was sent to the Arabs and Non Arabs, to All Mankind, in that sense. So we see what 'All Mankind' means. No need for us to go into assuming it means this and also that and maybe the other.
Has any other Prophet said this?
You nearly answered this yourself:
And regarding the Hadith with the 5 things, one of the 5 things states 'I have been sent [as a messenger] to the entire creation'
Although I have yet to see that hadeeth, what the Tafsir says is:
(I have been given five things which were not given to any Prophet before me, and I do not say it out of pride. I was sent to all mankind (their) black and white alike.
(I have been given five things which were not given to any of the Prophets before me. I have been aided by fear (the distance of ) a month's journey. The entire earth has been made a Masjid and a means of purification for me, so that when the time for prayer comes, any man of my Ummah should pray. The spoils of war have been made permissible for me, whereas they were not permitted for any before me. I have been given the power of intercession; and the Prophets before me were sent to their own people, but I have been sent to all of mankind.)''
Maybe brother this is why no other Prophet, nor Messenger, peace be upon them said this, because everyone else was sent to their own people, but the Prophet Muhammad, as he states, was given something not given to others, and one of that gift is that he is not just sent to his own people, the Arabs, but All Mankind, the white and black and brown and red.
Thats what 'All Mankind' is stated as being, nothing there about people before him, peace be upon him.
All mankind could mean all those presently living at the time the phrase is spoken, or at whatever time the referred to action takes place.
For instance, if the Prophet had said that all mankind would die in a nuclear holocaust, would mean that all of humanity that previously existed would have to be brought back to life, just so that they could die in the nuclear holocaust. But that at the time of some future nuclear holocaust, all those living at that time would die in it.
It depends very much on context. What was the context in which the "all mankind" phrase you are referring to was used?
The context is given, as you have stated there could be different views so it is essential we refer it back to the earlier people of knowledge, and the context is as given above that the other Messengers and Prophets, peace be upon them were sent to their own people, but Muhammad, as part of his special gift thing was sent to All Mankind as opposed to just his own people, the Arab.
It's pretty clear. 
