What's the best way to keep sushi fresh for the following day?
I think the issue is that your nori will get soggy if you make the rolls in advance and store them overnight.  Nigirizushi may be a better bet for making ahead.

Chirashizushi is an older style of sushi which is essentially a bowl of the sushi rice, with the garnishes either mixed in or on top. It should be well amenable to advance preparation.