If he expects, although he may not be sure, to have sufficient time to offer the prayer completely in addition to performing the ghusl before it before sunrise, then he should do the ghusl and perform the prayer.
If he anticipates that he has sufficient time to offer part of the prayer only before dawn after performing ghusl, then as an obligatory precaution he should perform the ghusl and offer the prayer even if some of it is after sunrise.
If he realizes that he will not be able to offer any part of the prayer before sunrise, then it is better to perform the Tayammum and the prayer before sunrise, and then perform the Ghusl and repeat the prayer after sunrise.
One can consider the fasting as valid if he doubts the validity now and there is a probability that it might be valid. The intention of fasting is not difficult to accomplish and it is correct from everyone fasting, since he has the intention as long as he is fasting.
The dua (supplication) is asking Almighty Allah. The imams of the Ahlulbait are intercessors to Almighty Allah and Almighty Allah does not reject their intercession. Nothing is wrong in seeking intercession from the Prophet and his household (peace be upon them). It is mentioned in the Holy Quran that Almighty Allah had said: â€œAnd if, when they had wronged themselves, they had but come unto thee and asked forgiveness of Allah, and asked forgiveness of the Messenger, they would have found Allah Forgiving, Merciful.â€ (4:64)