It depends a bit on your size and the board size. But generally, I would say at least the 74 I have is very easy and unproblematic to trim. I've set up the mast where I almost always have it, at 131-132cm from the tail and put the straps as I do on my EVOs, mid hold front and back hole back, since this gives me a spread I like.
The position works just as with a single fin, put them forwards if you like a looser feeling board. The standard 16cm fins work well with sails at least up to 5.5 and they are very good also in onshore and mushy waves since they give a lot of bottom end drive. Personally, I've ended up with the fins pretty much as far forward in the box as they go. But you can safely start out with the fins in the middle of the box if you want.
Sailing the board is easy too. If you are used to an EVO, you will have an easy time to plane early and go upwind well on the Evil Twin too. On the wave the board is also very easy to understand, I think. It awards the same kind of technique, but you need less power to initiate the bottom turn and you have a board that is much looser off the top. So in principle, you can be more sloppy with the setup of the top turn and still get away with pretty much anything. This means you can charge harder for heavier sections of the wave.
Good luck and ask again if you have more questions.