Taking your own movement into account when targeting?

It doesn't assume orbital movement nor enemy circling you. The only thing Guess Factor Guns assume is generally symmetric movement. By the way, PIF with Lateral and Advancing Velocity works very well.

No, it assumes that, as the way it scales between different distance & bullet power. Anyway, that can be overcomed with relevant attribute & more data.

Yes PIF with lateral & advancing velocity should work very well for similar reason.