You could try CS (or FAR)-23/25/27/29 and then filter down to the guidance material that is relevant to the desired class that the aircraft comes under.
In more general terms, here are some starters:
FAA AC25-11
FAA AC23-1311
FAA AC23-1309 (for compliance to the safety aspects)
AC 23-1523 (crew requirements)
GAMA Spec 10 and 12
The above should be able to send you off to other references useful but as Genghis pointed out you really need to define your aircraft class and role, as this will affect your requirements and cert basis.