Most people I know, self included, use just one strap. If I ever get good enough that I can consider playing box for gigs and dances and suchlike, I’m going to have to get used to using two straps because I hate sitting down when performing. (As a guitarist, I believe posing on stage is a VERY important consideration. 
) But the box is much less stable that way, and it’s not very nice to my hands either.
Re basses, one advantage of the C#/D is that the each pair of bass buttons play I and V chords in a particular key. If you’re playing a melody in D (in simplest terms, staying on the inside row), you can produce a viable bass accompaniment just using the lower outer pair of buttons, which give you D and A chords. That’s a start, anyway.
Anyway. Congratulations, and welcome to the dark side.