Before putting the body aside to work on other aspects of the bouzouki, it is a good idea to sand the inside.  Apply several strips of strong tape to the outside to support the staves.  Using a cabinet scraper that has been ground to a semicirclular profile, scape the inside of the body so that the seams between the staves are smooth.  Then sand the inside of the body with a rounded block and sandpaper, or a sanding disk on a round, firm foam pad attached to a flexible shaft drill press attachment.  The goal is to get the inside smooth, because uneven joints will break up the sound waves produced by the vibrations of the soundboard.  In a bouzouki, the body is more of a reflector, reflecting the sound waves produced by the soundboard back at the soundboard and out the soundhole (although on a well made bouzouki the body will vibrate, it just doesn’t really produce much sound in and of itself).  In a guitar, or other flat backed, instrument, the back and sides are more like resonating plates, which vibrate sympathetically to the top.  Be careful that any staves which were glued in with their edges not meeting perfectly do not get too thin between the scraping and sanding of the outside and inside.  It is better to leave a joint a little uneven on the inside, than to risk sanding the wood so thin that it cracks or worse yet, part of the stave is totally sanded away.  With practice and the experience of building a few instruments, you will get better at making the staves.