To be frank, this isn't a project we'd undertake because it's quite honestly easier to do the whole thing again from the beginning!
You have a few hurdles to overcome.
First would be product compatibility. Not all clearcoats will work on all basecoats... the solvents need to work together for good chemical adhesion. I couldn't guess which products would work. Some could even damage the original finish.
Second is your colour match... the orange is translucent in order that the silver beneath it reflects light back through it. Orange on silver is very different to orange on orange. No matter how well you colour match the product, you'll very likely just see patchy repairs.
If you do manage to get a blend of the colours that you're happy with, you'll likely find that the newer modern products you've used won't age and fade like the older parts of the finish so in a short time, you might see the repairs stand out even more.
For the most part, base coats and clearcoats have no anti corrosion properties so you'll be creating a barrier seal rather than preventing further rust and such.
Your basecoat products might struggle to adhere to the older product on the bike. A surface key will be helpful but it may simply scratch and peel off.
If I were to buy a mid priced airbrush for home use with easily sourced spares and basic functionality I'd opt for a NEO for IWATA. Gravity fed. We use high end SATA brushes a lot but for daily use but these £60-£70 ones are great for the price. A .35 nozzle/needle setup is a decent all rounder.
For clearcoat you'd need a bigger set up. I can't think of a time when we'd put clear coat through an airbrush for a bike... it would be too little product for us to work afterwards in the getting and polishing stages.
Multiple spot repairs on the substrate you've got is of course possible but I wouldn't recommend it as a DIY project unless you'd done a few others.
Hopefully that's useful information.