Cold is much, much better than heat for the tar (on the floors), for the behind rear bench, heat worked fine.
The pieces chip out instead of melting out, much cleaner.
FYI, Even a little tar residue will have an ill affect on the wire brush, wasn't fun.
I think some of the rust you have there looks worse than it is... and a grinder will help you.
When I started on my 2002, I didn't know much either, now I don't know much but I almost have a nice 2002. good luck.
for reference (the photos of rust on my 2002): https://flic.kr/s/aHsk9bDyAZ