Isn't instrument building an interesting and varied subject? I've made a number of cigar-box ukes, but I can't answer your questions, because I haven't a clue what you mean! I guess you are looking at it as an amplified uke. I only make acoustic versions, so the approach might be quite different.
Anyway, here goes, FWIW: If you are looking for a good acoustic sound, choose a box with a solid wood back, and use it as the front of the uke. You can remove the back altogether, and replace it with proper tone wood if you want to go that far. Thin the soundboard to at least 1/10th", and use a bridge plate and at least one cross brace. Arrange the neck/scale length so that the bridge is not too close to the bottom edge of the box. You want a clearance of at least 1 1/2" - more for preference. If you are serious about the tone, volume, and sustain, I'd advise you to remove the lining wood from the box, and glue the lid shut. The neck joint is very important. Keep it straight and level, and make it a very close fit.
If you are going to play it mostly with amplification, then much of the above won't apply.
There's nothing carved in stone about making CB ukes. It is about enjoying yourself, and learning something. If you do that, then it's a success.
Hope this helps.
John Colter.