5 overall states for email:
unread
read+star (urgent/reminder)
read (todo/reference for current tasks/projects)
archived (done + keep for reference)
deleted (done + not needed for reference, or ignored altogether) - so "your amazon order shipped" etc.
I don't keep the inbox empty, but there are only emails regarding ACTIVE tasks/conversations in it, its natural state is 0 unread emails, as if you don't do that, well chaos awaits.
Archive Tip; you can reply+archive; gmail resurrects the whole conversation if you get a reply back, so you can pick up the whole thing if something you thought was done with gets resurrected. (useful for those "here's an answer, hit me up again if that's no good" replies)
The flip side is; I don't bother with labels at all, search just seems to render that redundant as far as I can see.