The best way to get paint going is to fully strip everything. Its not that cost effective, but necessary if you really want to get the paint right. Since its not cost effective, and on unibody cars like these that you can't break it down easily to panels and frame etc. its often easier to focus on individual trouble spots.
The next bit of difficulty, your car is red. Red is TERRIBLE when its oxidized/faded and aged. You cannot just use the paint code and expect it to match, because it won't. Therefore for repair of spots of rust etc. its fairly common to match the color surrounding the repair, and then possibly spray many different colors if you repaint different areas of the car, its about the same as an aged white car, white does not = white...
Therefore the best approach for you is likely to remove all the trim, bumpers, as much as you can and then have the body work done, all rust needs to be removed as best you can (I use a small spot sand blaster on stuff I can do, holes need to be cut out and new metal welded in place, don't settle for tons of body mud, its not a repair its a coverup.
Paint is a huge topic, but there is plenty of information on google.
Powdercoating is far thicker and harder than paint. It is a more durable surface, but it must be baked on. Some people "home" powdercoat by baking in the oven, for large items like chassis parts etc. its common to have a place like a trailer/frame shop powdercoat it, the surface is too thick to use to finish body panels, and should be reserved for durable finishes on smaller parts. On engine components it can be very durable, but its not really diy.
Rubberized undercoating is a pain in the butt, I always just use por-15 instead, the rubberized stuff is hard to deal with but I often wirewheel anything loose off chassis and underbody then touch it up with por-15, and then if you want the same texture a spray can of rubberized undercoat does it. Por-15 hates uv so avoid that.
With painting cleanliness is key, no grease wax or oil can remain on the surface if you expect good results.
I believe there is a DIY for painting in the DIY segment. I would start there, and then ask specifics.