1) Preference really, but the rule of thumb is to use the smallest guide that gets the job done. Will it pass your knot? Do you Ice fish? etc..

2) Epoxy always. Color preserver only if you wish to preserve the original color of the thread used for wrapping.

3) Preference. I've seen guys use no checks, o rings, alum checks, vinyl checks. From my experience its more of a visual than functional decision.