Irvine did well for himself at Ferrari but that's not why he's wealthy. he put a lot of his money into property and I believe wasn't exactly poor when he joined.
I doubt Alonso would let Ferrari hire anyone who'd challenge him. hamilton and The Whinging Spaniard didn't get on an McLaren as Alonso clearly expected preferential treatment but Mclaren have never done that and probably never will. I suspect the Felipe won't get the whole teams support ever unless it's mathmatically impossible for ALonso to win the championship.