I'm limited in the number of knots I know but the 'Perfection Loop', as Bill suggested, is a strong small knot that won't interfere too much. As far as length, I'd say 5-6 inches but that's just an arbitrary guess. For storage you can use a fly wallet or any container that allows you to keep the fly + tippet straight.
Oh, you may want to consider placing one of those tiny stainless steel rings at the end of your leader where the tippet will be attached instead of a loop at that point. Attach tippet the same as you would a loop-to-loop but you'll have less bulk. Just a thought. Good luck.

Allan