I know this is a seriously newb question, but if Seltyiel has the ability to attempt to recharge a discarded spell at the end of his turn, does that mean that he effectively can get the opportunity to attempt a recharge check for a single spell twice per turn: first right after he plays it, and second at the end of his turn?
Yes, assuming he fails to recharge it after he plays it, so that it is in his discard pile. And also assuming that is the spell in his discard pile he wants to use his power on. Note he can only use his power once per turn, so if there are two or more spells in his discard pile, he can only attempt to recharge one of them. It also doesn't matter how the spell got into his discard pile. It could be there because he discarded it for damage or any other reason.