First of, what are the differences between a set-in neck and a bolt on?
Set necks are essentially like bolt on necks, except the tenon (two parts of wood that fit together) are much longer, and glued together. Likewise bolt on necks don't have any glue in the joint, and the tenon is much shorter, they are held together by screws.
set-ins have more sustain usually
Actually, if both joints were perfect, and the fits were snug. They would both have the same amount of sustain. An experiment by Cmogi (I think) from these boards was conducted ages ago regarding this topic.
what about if the neck has a contoured heel?
a contoured heel can be achieved on either form of neck. Normally contoured heels on bolt-ons aren't as ergonomic as set neck heels though. Since bolt on necks require a sizable chunk of wood to keep the bolts and the neck in place.
Ok, so the neck would be less stable?
Also, that would mean, if i was to order from warmoth.com, i shouldn't get a contoured heel?
another question is that which floyd rose would be a good idea to get? (original, licensed, scaller, etc)
Contoured heels are fine, don't worry about that. The contoured heels from warmoth are not like a contoured heel like an Ibanez Rg or S series. The Ibanez heel has less wood but is more comfortable and I like it more. Just my opinion. (Floyd Rose Question) Original but Schaller are good too