some advice from model making, dont start the building phase of a new project if you are stuck with one
if you leave something, left it entirely for good reasons like waiting to some new tool or something or you will be soon with a ton of half made projects
if you are inthe ending phase, painting and that i think is fine to begin another one
other method is do a lot of similar projects at a time
like that man that was doing telecasters like crazy, then you do all same phases at same time, cut all ones one after another, router one after another blablabla