Aslaamu`alaaykum bro
i will try to reply to your question to the best of my abilitiy inshaAllaah and hopefully more Knowledgable bros and sisers can reply with more detail and a better answer InshaAllaah..
To your first question i am not sure, but your question praying Istakharah salah i dont think would be valid without making salaah without the dua for it..
According to a traditional report transmitted on the authority of Muhammad ibn al-Munkadir, it was Jabir ibn 'Abdi'llah (may Allah be well pleased with him and with his father) who said:
"Allah's Messenger (Allah bless him and give him peace) used to teach us how to seek guidance in choosing the best option available in a practical enterprise [al-istikhara fi 'l-amr], just as he would sometimes teach us a Chapter [Sura] from the Qur'an. :
"'If one of you is concerned about some practical undertaking, or about making plans for a journey, he should perform two cycles of ritual prayer [rak'atain], not as an obligatory observance [farida], but voluntarily. Then he should say:
'"O Allah, I ask You to show me what is best, through Your knowledge, and I ask You to empower me, through Your power, and I beg You to grant me Your tremendous favor, for You have power, while I am without power, and You have knowledge, while I am without knowledge, and You are the One who knows all things invisible.
Allahumma inni astakhiru-ka bi-'ilmi-ka wa astaqdiru-ka bi-qudrati-ka wa as'alu-ka min fadli-ka 'l-'azim fa-inna-ka taqdiru wa la aqdiru wa ta'lamu wa la a'lamu wa Anta 'Allamu 'l-ghuyub
O Allah, if You know that this undertaking is in the best interests of my religion, my life in this world, and my life in the Hereafter, and can yield successful results in both the short term and the long term, then make it possible for me and make it easy for me, and then bless me in it.
Allahumma in kunta ta'lamu anna hadha 'l-amra khairun li fi dini wa dunyaya wa akhirati wa 'aqibati amri wa 'ajili-hi wa ajili-h :fa-'qdir-hu li wa yassir-hu li thumma barik li fi-h
If not, then turn it away from me, and make it easy for me to do well, wherever I may happen to be, and make me content with Your verdict, O Most Merciful of the merciful.'"
I personally do not think the prayer will be accepted if you dont read the dua, but for people who are not aware of how to make this salaah, they would need to study and find out what or how to do it , or else theres no point in doing it if its not done correctly. InshaAllaah i hope i helped a little bit...
Wa alaaykum Salaam