Yes, HPA is compressed air, it is also known as N2 in the paintball world.
No, your standard air compressor will only be able to fill it to a max of like 200psi, which even if your marker is low pressure operated, the Avenger isn't, you'd only get one shot maybe two on each fill. Air compessors that can put out 3000 or even 4500psi cost thousands of dollars. They do make a booster which allows you to effectively use a standard air compressor, but it costs a couple grand as well.
Yes, HPA will work in you Avenger, only Angels and some older markers meant to run on liquid CO2 can't use HPA. However, some markers work better with CO2 than HPA for some reason.