Putting music as a separate download doesn't really help. The episode still uses them, so you'd just be downloading the same stuff at a different time anyways.
What I'd do is shorten the music in
Audacity, which is as easy as highlighting the part you want gone and hitting the Delete key. Most music on YouTube (in my experience) is two loops long, so just shortening everything to one loop would roughly halve the size of the entire download by itself. But if you're going to do this, make sure you get the
LAME encoder so you can export it to MP3.
Music is the only concern when it comes to filesize. Level files don't even reach 1 MB unless they're enormous, and it takes a ton of graphics for a level's folder to even get near that amount.