You can't buy one that is too big or too powerful, unless you just can't fit it in whatever space you have. You can get creative and put it outside with a shelter around it, or up in the rafters, etc. and just work the power and plumbing from there.
If you plan to any sanding or similar (die grinder, polisher, etc.) or big painting projects then you really need to go big. Small jobs you can get by with a smaller compressor and wait for it to catch up. I'd recommend just to buy the biggest and most powerful one you can find and install.
I have a 17 year old Quincy portable 3hp 20 gallon and it continues to work nicely. I just bought a 60 gal 5hp Sanborn at an auction for $150 but I'll need to put in another 220V service before I can set it up. The Quincy will move to my hangar permanently now.
Check Craigslist and industrial auctions for deals on compressors if you're patient and don't need to buy new. Generally I think the older and more American the better, unless you're buying new Quincy or equivalent. A coworker just got a very nice 30+ year old Craftsman 80 gal vertical compressor and it is supposedly very nice. (auction find)