Just put your sheets on so it covers the floor and use your soffit to cover the 1 1/2 inch's at the top. Or add a small strip if it makes you feel better.....but do it on top....can hide it that way. Nice work so far man. 2 foot centers is fine. If there is no 2nd story then no need to be that beefy. Make sure to double up the top sill is all. If your putting the trusses on 24C as well they will line up with your wall studs and put direct load on the studs.

I build houses, garages, sheds and ice fishing shanty's......but no man caves just yet. Will be building something similar at camp.

Keep up the good work,
Kevin