Been there, done it all. I've been airbrushing and painting cars, motorcycles, helicopters, helmets, zippy lighters... and just about anything since I was a kid. I could always draw like I invented it, and hated the fact that my work had to be hidden in filing cabinets after all that effort or else the graphite would smear. So, a more durable genre developed.
You're experiencing what stumps most people when they start... and that is paint chemistry. I had to take classes on it specifically in college, not to mention spend years learning from the established guys, and my own trial and error.
You've got an aluminum frame? If your bike is new and you're changing the paint scheme, remove all the decals, and lightly sand the existing finish. It's the best bond you're likely to have, and the existing finish is a fine foundation. Then, a coat of sealer, which basically just means to bring the bike to a uniform color. Black or white is usually fine depending on what your final color will be. White for a light color? Black if it'll be dark. Only really exception is candy paint (silver for cool candy colors, gold for warm colors).
If it needs to be taken to bare metal...fine. Don't sand it though, you'll be there all week and it's a mess. Instead, go to a local carwash, soak it with "Easy Off Aerosol Oven Cleaner" and wait 15-20 minutes. Have a beer. Then, pressure wash it. BOOM, bare metal. That easy. (OH, don't wear flip flops.😬)
Next is paintint. Most automotive finishes are two-part paints with a catalyst and a harder. You want a 2-part etching primer for bare metal. It's available in cans with a res button on the bottom. Slapping it on a tabletop pops a bladder inside so the two mix. Shake like hell for 10 minutes, and follow directions. Here's a satin black from Eastwood https://www.eastwood.com/2k-aero-spray-rat-rod-satin-black.html
Color and all that can easily be applied with whatever paint you want. Testers model paints even has a flip-flop color shift in an aerosol can. But you can use createx airbrush colors through a cheap gun... or whatever. The sky's the limit.
Finally, add decals if you like (sets available on ebay) and then use the same 2 part puncture can for the application of the gloss clear. BOOM. DONE. https://www.amazon.com/USC-Spraymax-Matte-Clearcoat-3680065/dp/B0178ABUVM/ref=asc_df_B0178ABUVM/
Keep in mind that flat and matte paints are nearly always powder coated or baked on. For your flat black... I'd go to Harbor Freight and pick up the powder coat gun and a bottle of flat black....then get industrious with some scrapped kitchen ovens and make a little enclosure to bake them in. But that's me.
Good luck.