Hi Stuart, welcome to the forum.
To answer your questions in order
1) some people leave theirs on (you can get it to turn the front display off when idle). If you decide to turn it off then please shut it down properly, dont just turn it off. Note when idle, if there is compression to do this is when it does it.
2) the B2 will only apply compression to WAV files it sees on its HDD. Therefore your Apple format files will not be touched by the B2. It can play some Apple formats but not all.
The 'normal' format used on a B2 is FLAC thus if you can convert to this before loading, this is best. However WAV files are OK and the B2 can convert these to FLAC.
3) sorting files. The B2 does not use any music tag information that may be embedded in the music (although it does not mind this information being there). When loading and storing music the B2 uses the directory and file names used to organise the music. Artist/Album(CD)/Tracks. So I think the answer is no.
4) the "Export to USB A or C" backup function is INCREMENTAL in operation - new stuff is added to the backup.(but deleted stuff is not removed).
Fred