painting is in the prep, for anything.

The question is what type of paint job are you looking for?

If you want it to be perfect, you have to get it down to bare metal, otherwise you will see blemish with any little bit of leftover paint

IME chemical is the way to go for on occasional paint job

also remember painting a frame properly takes a ton of time and is more expensive that you would think

rattle-can that you can find in auto and hardware stores can produce a fantastic finish, but it is not at all durable, auto paint is durable but more difficult to use, expensive and even more hazardous than rattle can

first you have to have a good mask

then

bare metal, acid etch primer, sandable primer, multiple color coats, and multiple clear coats

personally any more, I would a) keep the patina, and maybe clear b) send to powder coat or c) if it is a super special frame send to a good painter (noting that if it is any sort of collector bike, refinishing will reduce value