It's odd about hte 20+ eggs. That's a lot! You probably don't really want to get that many.
I don't see why they don't wait and see how many embryos you have at day 3 before deciding whether to try for balstocysts?
Anyway, personally, I would not transfer ttwo unless I'd had several failed cycles already. The risk of twins is quite high, with all the attendant risks to your preganncy and babies that comes with that. (that said, I do understand the appeal of getting two for one) And I think most clinics would not transfer two at once unless you've had several failed cycles and/or you're older.