It is a 3.7HP (running) motor. Since I am not doing any ultra high PSI work, I was thinking of staying single stage. My rationale is that the 2-stages are great for high pressure, but I am not needing a 175PSI system---plus you only have it "in storage" until it is depleted and then you are at the mercy of a vastly reduced CFM rating. A 5HP Dual stage puts out fewer CFM than a single stage--mainly because it is wanting to do it to a higher PSI. But "keeping up" cfm, it produces less for a given system. I am NOT a pump expert, so if there are added benefits that outweigh this, I truly am all ears!
As for cool air, my system is running the air through about 40' of black pipe (some folks use copper) that runs across the ceiling and then down the wall into a drain fitting with the air take off fitting about 1' up that then runs through a water separator above that. I painted (HVLP) my 90 with this set up and it worked out just fine both on temperature and H20, but all good advices. My sandblaster doesn't mind my set up, just minds the CFM rating at times... So most likely will continue with single stage but am not theoretically opposed to a dual stage. Does it keep air cooler/dryer?
I know I can get a 2 cylinder or 3 Puma pump, a 5HP (running, not peak) motor and keep it under $1K. That is what I was thinking. I will check my tank, but last I checked I am good. I regularly de-water my tank, so I am ahead of the game of some that way (been meaning to put the auto-discharge port on it...). I have a hose permanently attached and I open my ball valve and drain right into a bucket often enough. Rust happens, but so far so good. I put two alkaseltzers in the tank every 6 months to convert all the rust to a rock hard coating.
I am kidding about the alkaseltzers. However, now that I said that out loud....It wouldn't be bad idea to slosh a rust converter through it from time to time!