I would suggest not making a decision until you reach key milestone in your build. Avionics are changing too rapidly. In the RV-8, both servos go in the fuselage so you don't need to make a vendor decision until that part of the build. Then, wire to the panel. Once you get to the panel construction, you can decide what head-unit you like (dedicated or integrated or EFIS).
I added my AP to a finished RV-8 and it was not difficult.
Do you want redundancy, or are you okay with the autopilot depending on the EFIS?
nope- roll servo is in the wing of the RV8