Several things you want to look at
What is compressor powered? Gas or electrical? Electrical ones are getting popular, but they do suck up 15 amp. So you are going to need dedicated power outlet and most garages are not really designed to have this.
Compressor should be about 20 gal. 30 gal+ if you need to run air sanding grinding
Each air compressor has CFM. Most air tools are powered by 90 PSI so you want to look at what CFM it gives at 90 PSI. You want it to give you 4 CFM or more – this is what most impact wrenchs require and if air tank cannot deliver least 4 CFM the air tank cannot keep up and it can burn out the compressor motor.
Air hose – no longer than 25 feet, longer it gets, more air power you would lose. if you need to run longer, then you want to attach air line to a metal pipe to reduce the rubber/polyerthane hose run.
Air impact gun – look at CFM and find the one that has good balance of air efficiency (low CFM) and power. Generally most of top ones are made by IR. Most of the cheap wrenches are also powerful enough but terrible air waster
I run Sears 33 Gal compressor with IR-2135Ti. I can work comfortably without tripping the power or burning out compressor. Using a grinder, the air compressor kicks in every 2-3 minutes so it is not really good for doing body work but gets the job done.