Assalamu’Alaykum
For your questions Iqbal_soofi :
First Question:
Ibn Al-Qayyim (may Allaah have mercy on him) mentioned three opinions concerning the circumcision of the Prophet (peace and blessings of Allaah be upon him). He said:
There are different opinions on this matter:
1 – That he was born circumcised
2 – That Jibreel circumcised him when he split open his chest
3 – That his grandfather ‘Abd al-Muttaalib circumcised him according to the Arab custom of circumcising their sons.
source:
http://islamqa.com/index.php?ref=31069&ln=eng&txt=circumcise
Second Question:
The first person to be circumcised was Prophet Ibrahim (alahis salaam) .
Abu Hurayra said, "Ibrahim, may Allah bless him and grant him peace, was circumcised when he was 120 years old. Then he lived eighty years after that." ( Bukhari )
Sa'id ibn al-Musayyab said, "Ibrahim was the first to be circumcised, the first to give hospitality, the first to trim his moustache, the first to cut his nails and the first to get white hair. He said, 'O Lord, what is this?' 'Gravity,' Allah replied. Ibrahim said, 'O Lord, increase me in gravity!'" ( Bukhari )
So anyone after that who followed Ibrahim, Isa, Musa ( allahumus salaam) all practiced it, and even now you see that male circumcision is practiced in Christianity and Judaism. But at that time those who followed Isa and Musa ( allahumus salaam) were considered Muslims, because they submit to the will of Allaah as they were taugh to do so by their prophets at their time.