Hey Andy, greetings. My specialty is actually INSIDE the tub, but I think I can give some tips on the outside. I refinish tubs, but sub out the ext refinish to a sandblasting company. If you're planning to refinish it, I would suggest you either have it sandblasted or forget about doing it at all. If you're up for it, you can rent a sandblaster at a hdwr or com rental shop OR you can have it done. If you have it done, just ask what they'd charge to refinish the whole thing.
The outfit I use sandblasts it, primes & paints 2 coats. I'm not sure whether they specify latex or alkyd based paint though, and I'm not sure that it matters. I guess if I were doing it, I'd go with an alkyd base.