if my memory serves me right, the handbook has a list of settings for background2 ini files under "parallaxing backgrounds". the rest can be found within the "data/_templates" folder of your smbx2 installation.
as for music, it depends on what kind of music you want. good resources for high-quality video game music are
vgmusic and
khi. do note that vgmusic supplies midi files so unless you know how to work with soundfonts those probably won't sound too good. for other music, it's always best to look for a download supplied by the original artist. third party services that allow you to rip audio files from sites like youtube do exist, but giving credit and respecting the wishes of the original artist is always important.
do also be sure to convert any songs that are in the mp3 format to ogg using a program like audacity, as that format is lighter and supports
clean loops.