You may find that the electonics is the easy part of making an autopilot! Assuming that the RC servos have sufficient power to drive your control surfaces, and that you are able to over-ride them when needed, figuring out how much control surface to use in any given situation, and for how long, is the tricky part. I don't know of any on-line resource that gives a good description of the problems involved.
For a heading or track hold device, you may like to consider how much bank angle will you use to correct a given heading deviation? How much aileron will you use to achieve that bank angle at 70kt, at 100kt and 130kt?
For a pitch device, are you holding speed or altitude? How much elevator do you use for small and large height deviationsat various speeds? If the power is reduced are you going to maintain altitude at all costs (until the airplane stalls)? If you slow down/speed up a lot how will the autopilot tell the pilot is significantly out of trim when the autopilot disengages?
Capturing your aircraft's flight control characteristics may be one of the most challenging aspects. Best of luck with the project.