I'm about to embark on similar rust repairs to the rear of my sills, following an MoT failure a few days ago. My tester wasn't quite as generous as yours, obviously!
The big thing with rust is to nip it in the bud before it spreads, even if you just spray rust neutraliser/converter in/on those panels for now so they don't get worse before you get time to repair it properly.
Those bushes don't look too bad, it's the subframes that would bother me to be honest.
As for your brake imbalance, chances are the sliders and/or calipers have siezed through lack of use, you may find driving it up to ~30mph and hitting the brakes hard a few times will help "rebalance" them but also try driving along with the brakes lightly applied before doing that. The heat generated will help shift the stuck calipers/slides.
Very true but that's why we're all here, it is something different from the Euro-blob norm that so many people blindly accept as cars these days!