Is permissible to buy/sell with non-Muslim?
Yes buying/selling for a Muslim with non-Muslim is permissible as regards what is lawful.
Is it permissible for me to name my newborn baby boy “Al-Moustafa” ?
There is no harm in naming your son “Moustafa” without using the ”Al”.
How many pieces of cloth are used to enshroud a deceased man, and a deceased woman?
A deceased woman is enshrouded in five pieces of cloth: head cover, wrapper, shirt , and two folds of cloth. On the other hand, a deceased man is enshrouded with three pieces of cloth.
Is a woman`s prayer considered invalid if non-Mahrams (marriageable men) saw her offering it?
A woman`s prayer isn`t invalidated if non-Mahrams saw her offering it, but she had better pray in isolation.