Touch up the front bumper yourself.
No, do not just slather on a ton of bondo on the door, pull the dent and then a minimal amount of filler if any. Otherwise, it may just come off in a clump, but I am assuming you intend to keep it long term, not just hide things to sell it.
I have no idea how painting the driver's side door does anything to blend the paint. Did you leave something out?
Paint the rear bumper, your picture is not detailed enough to determine, whether it just needs touchup or a paint job but it also depends on how picky you are.
You cannot sand that rust down. The rocker panel is shot and will need new metal welded on for a long term repair. Anti-rust spray is just a waste of time at this point, unless you are just trying to hide it to sell it ASAP.
At the same time you are asking "won't the rust just come back after a few years", well of course it will even in the best case of an attempt to restore to like new with an aftermarket job, because even the factory metal/paint, rusted in a few years. The back of the panels will need rustproofed, or it won't last as long either.
It is decision time. $1100 is not that much, but it depends on the quality of the work, how much time that buys you, and how much time you need, how long you intend to keep it if it were restored to a more or less, low blemish condition. I would chance it if you figure you'll sell it in a couple years but if you intend to own it to the grave, then there's the other aspect of vanity, that touchup or DIY can work for the paint spots but the rust would need a new panel welded on.
You did not mention the mileage on the vehicle, nor can we see the undercarriage to assess total vehicle fitness to plan long term. If the unibody frame/structure on it is rusting as well, then I would spend the minimum possible on it to put in a sellable state and get rid of it. If it is only the rust you pictured, which would be unusual but I suppose is possible, then it is worth paying someone to weld on new metal. In particular look at the engine subframe mounts and the strut tower mounts, those two are significant problematic areas that bondo can't fix even for a little while.