Unless your going to paint metalics, why waste your money on base/clear?
Primer:
Over raw steel, PPG makes an etching primer, dont recall the name of it.
Over existing paint: PPG makes a primer/sealer
For sandable primer: PPG K36 high build. Stuff is like sprayable bondo!

For topcoat:
I use PPG "Concept" Its a Acrylic Urethane single stage paint. If you feel you need for some reason, or have to have clear on it, you can go with single stage color and clear. AKA, same reducers, same hardeners AKA, less product=less money.
Stuff is about bullet proof.
A quart of paint will be enough to shoot your entire bike twice if you need too, including the frame.. Just the tins, a pint would do ya...IMO..
PPG store will hook you up with the right amounts of reducer and hardner.
Ask for sticks and strainers when they go to ring up your sale. They should give them to you for nothing.
AND, please!! wear a resperator when shooting the stuff as it will screw you up. Has isocyanates and all sorts of nasty crap in it. Causes nerve damage, cancer, etc....
P.S. Be prepared for sticker shock....