I'm no pro but did my own so here are some things i learned...
You dont really need to sand all the clear off...just get the major ding's, bang's and chip's squared away and feathered out sanding wise....you really just want to "roughen" up the old clear so the primer can adhere...
Yes you want to prime the entire car with a good self-etching primer...this lets it adhere to the old paint....you just paint over old paint/clear and odds are it'll flake in due time....primer is a must do...
I used Hi-Build primer....it helps fill the minor imperfections and sands way easy...a big plus !!!
Prime then "guidecoat" your panels or parts....this lets you know when things a good and flat and blended when you sand...you can pick up low spots easy this way...just prime a panel, then dust it with a light coat of spray can Flat Black...then start sanding til the "guidecoat" is gone...works the balls for us novice's..
Once done and ready to paint you wanna put a sealer down to....we primed to get everything where we wanted..final cleaned....then shot the entire car with sealer...your sealer is applied just before the base...let that "set" per the instructions then go to town on the base....
I think the only thin I used sealer on was the entire body....the single parts were just primed/cleaned/based....
The pic is just before paint....this is cleaned and ready to shoot....we nailed it with sealer, Black...let that air out and hit the color...
Paint early the morning as the bugs and such are not really out if you doing a garage job....we started at 7 in the morning and at 6 pm rolled it out...