Hamkid, Please don't take offense, but I believe that at your stage of mechanical learning you might be better off without an impact wrench. I have overhauled many engines and transmissions without one. I do have air, and always have, but I have seen a lot of damage done with impact wrenches. Admittedly, they make the job go faster, - that is not necessarily a good thing.
We all like seeing someone get into fixing their own stuff, so keep at it.
If you do end up buying an air compressor, I would recommend against the direct drive oil-less. Buy one that is belt driven. 2 belts are better than one. And if you find one that you think will do the job, buy the next size larger. There are a few variables wrt cfm and pressure. Shop carefully. I was called to someones house not long ago because his impact wrench wouldn't loosen his wheel lugs. His hose was only 1/4 inch and the air compressor was marginal to start with. Loaned him my hose and it zipped them right off. Not all impact wrenches are the same and it has been my experience that the inexpensive ones with unfamiliar brand names will not come close to the advertized torque.