Well, nights of better seeing (as opposed to the Knights of Better Seeing - the name by which they were known before they were the Knights Who Say "Ni"
) are best for collimating. I guess the "twinkle" test is easiest to pick a good night - I'll try and find a link for some reading material. I use an artificial star for initial collimation (especially if I've cleaned the corrector, which I do when removed) then do fine adjustment with a bright star. Bob's Knobs definitely make it easier.
There are two schools of thought about whether to collimate with diagonal in place, given the diagonal can potentially be a source of problems. I've tried both and found no appreciable difference, but your mileage may vary.
As far as cooling/comparison goes: Paul Haese has a C14, which he adapted for Peltier cooling, and he should know more about the specifics of that scope than I do.
Edit. Here's an article about measuring seeing, though I admit I don't think it's as clear as it might have been:
Astronomical Seeing
There's a table half way down entitled, "ratings on the standard scale of seeing" that has the "twinkle" scale on the LHS.