Hmm, I can set gain up to 400, but at that gain it generates soo much noise, I don't it is usable, at least i would need several thousands of light framses to avarage that out.

Do not beleave in any "magical" algorithm that removes noise with dark or flat or anithing else. Dark is removed from every frame, right? No random noise (in the light frame) can be eliminated by removing a static "dark" frame! It can eliminate anything that is permanent on your sensor, such as hot pixels. But nothing that is random in nature. Similar storry with light frames. It can eliminate faults like pathces from dust on the sensor or vignetting, but not random noise.
I have experimented with dark and flat frames but i don't see that dramatic effect.

Rotation is an inevitable issue, I agree, and there are parts of the sky where it is more paiful (zenit) and there are parts where it is not so painful (lower part at the southern sky). I deal with it by crop. Just as with the migration during tracking. And as we anyways need to crop to the middle of the frame, vignetting is not as much an issue.