Mate, you've really taken on a MAJOR project for yourself...good luck.
Can I make one TEENSY suggestion. I work in a full motion simulator at the moment, so what I'm about to say is genuine (no sarcasm, seriously).
People who make simulators are generally not pilots and thats what leads to simulators not behaving like real aircraft. If you were a pilot and a software engineer, you'd probably have a better chance of getting it right, but those two fields just don't seem to go together here in the real world (thats my observation anyway).
What I'd suggest is that (a) you get yourself at least SOME time in the aircraft type you want to emulate...have a FEEL of the trim, talk to the people who fly it and have them show you how all the bits and pieces work...the investment will probably be fun and will save you pulling your hair out in clumps trying to figure out what we're saying in PPRUNE. (b) dig into the systems books...as many smart people as there are in this forum, you're never, NEVER going to get the right formula for this without doing both a and b above...again, my opinion and not meant to deter you in any way from your project.
On the SAS question, some flight control systems have both inner loop and outer loop systems. Inner loop inputs arent felt in the controls (ie a gust of wind will be corrected for but you wont feel it in your cyclic or pedals)...outer loop is stuff you'll feel feedback through the controls (maybe an altitude hold...if altitude is low, the collective will actually move up to correct)...now this is a GROSS generalisation and I'm sure it has no bearing on your specific aircraft type (which I know nothing about).
Happy to discuss further...and good luck.
HP