Painting Advice

looking for some painting advice. I am starting to get ready to paint the engine compartment on my 66 Dart. My first attempt at priming didnt go well with the gun and the primer I had from a job someone did for me a year ago. I bought a new gallon of primer and decided to buy a new gun as well. Summit had a nice kit made by devilbus called starting line. I bought it but wanted to see if my issues the first attempt were gun or old primer. Well it didnt take long to decide it was gun so I switched to the new gun and wow, what a difference. I put on 2 heavier coats of primer tonight and I hope to sand and hit it one more time before attempting paint and clearcoat this weekend. Here are a few prep questions I have about mixing. Tonight for me to do the engine compartment I mixed 4 parts primer to 1 part activator which made just over a pint. that just did the area I had prepped. When I do the base coat should I mix the same amount or will it go farther then the primer? Also as I go to the second or third coat of the base do I dump any extra out between coats or can i just add to the gun again? If its going to take the same amount of paint for each coat do I mix all 3 coats for base up at the same time or mix them between coats? If between coats do you clean the mixing cups after each batch or just use multiple mixing cups so you can read the side as you mix? Can the gun sit between coats or should I run some thinner thru it between coats to keep the needle as clean as possible?
now as for actual painting I can tell from spraying around the shock towers that distance away from surface is critical. what is the best method to work around an area like this your hand holding the gun?
What should I know before I attempt the clearcoat after the base coat. I realize that the clear will be the most critical for a nice finish.
Thanks for any advice you can throw my way.
Rod