I'll try and answer where I can:
I use rudder to aid in roll (initiating roll, not really roll rate) and in firing mostly, though some people use it more. Rudder use tends to cause lots of side-slip, which is very draggy, so limiting rudder use is good unless you are looking to slow down quickly. For firing, fine-tuning your aim with rudder is almost a necessity.
Your second question about the FM2 vs. 190, it depends on a lot of factors. All aircraft in AH have a turn-rate/radius that changes with speed. Some aircraft have better turn-rate at high speeds, some at low speeds, some at very high speeds. The 190's tend to be good high speed turners, but poor low speed turners. The FM2 is pretty good at most speeds though holds no advantage at high speeds. Your decending spiral ensured high speeds which played right into his hands. If you'd slowed the fight down a bit, depending on 190 version you were facing, the difference in turn rate may have been very significantly in your favor. If you could have equalized E, then slowed things down a bit, you'd likely have pulled around on him if he didn't decide to try and run.
-Soda
AH Trainer Corps
The Assassins.