I second enlisting the help of an electrician, if for nothing else a working knowledge of the electrical codes. I assume you are in the US?
I know you for example plan to power a welder and compressor, however, any garage outlets must be GFI protected. Additiopnally as to power to the garage using AWG 12, 10 or 8 will get you 20, 30, and 50 amp service respectively. However, if the run exceeds 70 feet in length you need to go to the next larger wire size to compensate for voltage drops under loads.
For 240 VAC service you need to run 3 conductor cable with Ground (4 conductor total). If you are planning to bury the cable there is a whole new set of rules as to depth depending on cable type or if a conduit is run. Likewise rules for overhead runs.
Depending on location the work can be subject to inspection including in progress inspections. The NEC (National Electric Code) gets pretty specific on most of this stuff which is the main reason I suggest a qualified electrician. If the work is not done to code and results in fire or injury your insurance company may not want to know you.
Ron