I can't say I know a lot about the subject, but a friend of a friend donated eggs once for money. She had said she had to take hormones/ fertility drugs for about a month so enough eggs would mature. Again, I'm no expert, but since T shuts down ovulation in most cases, I'd imagine you'd have to be off it for at least a couple months before they'd even consider pumping you full of the fertility hormones. I'd inquire with whatever service you'd be using for the harvesting though, that's the only way to know for sure.
As for pain, the girl I know said she was heavily sedated for the entire retrieval procedure and doesn't remember it much.