Do you have 240V power 'available' in the garage area? Or do you only have 120V?
(technically, you 99.9997% probably have 240V power, but you may or may not have an outlet for that 240V power in the garage.
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If you are limited to only 120V power, well then that is your limit. Which means about 5 cfm @ 90 psi is all you will get from a 120V powered compressor.
Notice that I haven't mentioned "gallons" at all.
More gallons of stored air just mean that you can use the air tool for a little longer before the compressor kicks on and starts to (try to) refill the tank. More air (higher pressure and/or more gallons) in the tank means that you can run the particular air tool for a longer period before you 'run out' of air.
Just how much longer will more tank capacity get you? It depends on just how much air the tool needs/uses and how you use that tool.
Air impact? Usually that is a tool used for a few seconds at a time, and then you are doing something else and the compressor can refill the tank while you are doing that (but not always).
Filling a tire with air? Usually not a 'time critical' task, so waiting for the compressor to refill is usually not that big of a deal (but it is or can get mighty annoying!).
Air blow gun to blow off dust or water or whatever? You might drain a 20-30 gallon air tank in a minute and then the compressor kicks on to try and refill the tank.
More tank capacity and more motor power running the compressor lets you do 'more'.
Your call as to how much you want/need.
But if you can do so, a 60-80 gallon 3-5 hp 240V compressor can let you run almost any air tool you might want/need in a home use situation.
With a 120V compressor, you WILL be limited to what and how long you can run some air tools. Which can either be annoying or it can make the tool basically 'unusable' for you.
example time:
Spray guns typically need a pretty good amount of air.
Media blasting (aka 'sand blasting') can use a lot to a LOT of air. Blast for 30 seconds and then having to wait for 3 minutes for the tank to refill and then blast for 30 seconds and then having to wait again, to me makes this use scenario in the Nope-it-don't-work category.
Air die grinder? Again, with the small 120V units, you will be able to use the tool for maybe a minute or so and then have to wait for the tank to refill.
Look at the tool(s) you have or might want to use. See what their listed CFM air usage is (something like "4 CFM @ 90 psi" is a pretty common 'small' air tool listing, like for a 1/4" air die grinder). Then, for 'most' tools, you have to multiply that number by 4 (because of the 'duty cycle' way that the air tools are listed under, many are calculated on a use-cycle basis of 15 seconds on out of a minute).
So that die grinder that was listed as needing 4 CFM @ 90 psi actually needs more than 16 CFM @ 90 psi to run continuously (and the way I use an air die grinder, I use it waaaay more than in just tiny 15 seconds bursts).
The hot dog or pancake style air compressors are more suited to running a small air nailer than running 'mechanics' air tools IMHO. They can fill tires just fine, but depending on the tire you may have to 'wait' for the compressor. A quick burst on an air impact, sure. An air die grinder, nope. And air hammer, probably not. A spray gun, probably not unless it is an airbrush sized one .
YMMV.
