Utwo, if I were you I'd start with a 6". It's still not much glass to push, and I feel the extra aperture would be worth it. I once made a 4" mirror and actually found it a bit too small in my hands for comfortable work. Just a personal opinion, though.

And like just about everyone else here suggests, find a copy of Texerau's book. I built my first scope using the original (haven't seen later edition) and it tells you just about everything you need to know.

__________________
The Devil offered me power. I told him I preferred aperture.