Like others said, it depends on your gun. The gun I last used (DeVilbiss FinishLine), it needed 13CFM continuous. That goes down if you take breaks.
If you're priming the whole exterior in one go, you'll need all 13 CFM. If you are doing smaller pieces at a time and don't need to maintain a wet edge over large areas, you can probably get away with as low as half that.
Tip size doesn't affect anything related to the compressor. But it is important to match it to your paint TDS.
Compressor tank size just controls how long you have until the compressor kicks in. If it won't keep up then you will need to stop spraying until it catches up. With my 80 gal tank, that was about 10s of spraying. HVLP use a LOT of air.