What type and size air compressor (HP, Tank Size, CFM, direct drive/2 stage... etc) would be suitable for a home garage where I'm going to do small amounts of maintenance but nothing major?
So I would need to be able to use a tyre inflator and a impact wrench, I'd like to be able to do small amounts of spray painting but I don't plan to respray an entire car.
(I'm not asking about specific brands or a models, I want more general info than that)
I would suggest looking at the tools you plan to purchase for use with the compressor.
Air tools will list what CFM @ X PSI they need to operate.
That is the most important number, to make sure it can supply the air flow your tools need to run.
Beyond that, horsepower and tank size are going to be how much money you are willing to spend.
A larger tank will be able to supply air for longer, higher horsepower will be able to fill a tank faster.
Horsepower typically goes up with tank size otherwise the fill times would get severely long but check the ratios of Power to Size. For example I've seen a 2.5HP 8 gallon and a 2.5HP 10 gallon in the same product line. So in that case, the 8 gallon can fill faster and was actually rated to provide higher CFM.
Inflating tires, pretty much any compressor can do.
Impact Wrench (guessing that is what you mean be Rattle Gun) I've seen call for 3-8 CFM @ 90 PSI depending on drive size, torque rating and manufacturer.
Air Ratchets, I've seen 3-5 CFM @ 90 PSI.
The tools that really eat up your air supply are the ones that you keep on for longer periods of time such as grinders and cut off tools. An impact wrench should do its job with a couple quick pulls of the trigger whereas a grinder you can have on for several minutes at a time when you are working on a piece.
Painting tends to use a lot of air (CFM) at low pressure (<50psi, typically). So do sanders. Air sanders are great if you are planning on doing bodywork of any kind.
Review your air tool requirements as @ManiacZX recommends. Painting is an enjoyable activity with challenges; getting paint that matches exactly is almost impossible. You will need an oil/water separator for tools like paint sprayers and sanders that run much longer than most tools.
For small- to mid-size jobs, such as operating air impact wrenches, air pistols, and maybe some moderate spray painting, I strongly recommend a portable double hot dog air compressor where I believe the Makita MAC2400 is the market leader, at least the one I have. I have only recently been using it for automotive purposes and before I used it for extensive home remodeling, including framing, hardwood, roofing, trim and other types of nailers.
It currently sits in my shed, which I have mostly been using for automotive work. There are many people who will over-advise the size you need claiming that you need at least 40 gal 150 psi tanks to run an impact wrench but, for most backyard mechanic purposes (for maybe taking off lug nuts or really stubborn bolts once in a blue moon), a small one like this will do just fine. Don't buy into the bigger the better philosophy of many people in some societies (not to name any names but you can guess who I'm talking about. The same folk that buy F250 just to go to the supermarket and back).
