My 10c - when painting wheels ABSOLUTELY you must paint the inner surface. I have just had a set of 8 x 15 rims blasted as they had heavy rust, but I hate throwing good stuff away ( apparently 8 lug 15's are difficult to find now ?? ). The rims were primed in a cold GAL primer, that is a good base to stop future corrosion. I usually paint the wheels all over ( including inside ) in a semi gloss black, and then spray the outer surface in colour. Most 6 and 8 lugs I re-do in an off white to replicate the OEM factory look. Some over-spray into the inner rim is fine, and replicates the factory finish on many trucks back in the day. I started doing it this way when repairing old tractor rims to protect them and give them longer life. I have had to chuck a number of old rims because after removing the tyre, the inner bead is too rusted out from water and salt corrosion.
Also - you can get good results cheaply using an airless sprayer, a tin of good quality tractor enamel and some thinner. Just turn the spray right down, and spray thin coats, Warm the paint and thinner first, and keep the rims inside before painting if its cold. That way the paint won't run.
Not sure what colour these are going to run yet .....