There is no setup videos for 3.2.1. And 99% of the major improvements for helicopters were made in AC3.3 for ease of setup. Like in 3.2 HSV_MAN only has two settings - 1 and 0. 0 turns on the PID controller, 1 turns on manual direct to stick so you can set up the head. In 3.3 and later there is five settings for HSV_MAN. And no collective curve settings for Stabilize. But the basic head setup, mechanically, is the same.
The current wiki on tuning was actually written back in the APM days, so remains the best current online reference there is for APM and 3.2.1. However, there are even improvements to the tuning method now being used and the wiki needs to be updated to reflect those.
The APM, although it is a very good board, is considered non-supported anymore by the ArduPilot community. I have a lot of experience with the APM on Trad Heli's so can try to provide some pointers on how to get it to fly better. But I would need to know some more specifics as to what problems you are having, along with a current exported .param file and maybe a flight log. Since you have an APM 2.6 with no internal compass, and the last I heard you were not using a GPS/compass module, it could be that's your problem because you have no compass?
Seeing the .params would tell a lot about your setup.