Halfords are your friends here. Their paint is (relatively) cheap and good. As said, not the best time of year, but it has it's advantages (no insects to stick to the wet paint). I would not recommend any aerosol painting indoors, even though I presume it was a tongue-in-cheek comment.
I have painted many aftermarket 'bits' to put on cars. Just sand the surface gently to give the paint something to adhere to. A cheap primer, then top coats. Once completely dry a couple of coats of lacquer to make it shiny. You don't need to rub down between coats IMO (all that does is potentially leave bits on the surface and just takes more time and paint).
I found the secret of 'rattle canning' anything is to not go mad. Multiple thin coats give the best finish. And make sure the spray nozzle is clean each time; any gunk around the nozzle can make it 'splatter' which will ruin the finish. The can needs to be fairly warm or the pressure of the propellent will die and you get splattering.
And an insect-free environment is a must! For some reason small flying things love the smell of new paint and can't wait to land on it, which will ruin the job, so you have to start over.
I painted the front splitter and rear diffuser on my F33 with Halfords gloss black rattle cans as they both came matt:
