Streets, you got a huge shop compaired to most of us here. Me, Matt and Truckguy probably don't even have our own garage at that... our parents own the things not us and they are small. Plus we don't have as much money as you. As far as a 15 gal 5 HP compressor working... mine won't. It run's constently when just using the blow nozzle to dust something off... Well I can use the air for about 2 minutes and then it kicks on. Paint in the ass, and my other small one that my dad uses on jobs for nail guns, etc I don't even touch. But anyways, Truckguy, before you even weld anything I think you should try and find scrap metal somewhere and practice a ton before you weld anything like a frame, or anything at all that you will be riding in. Try different welds like butt welds, etc. You can lay a nice looking weld down maybe but it may not penetrate well so test it own. Butt weld something, put the piece in a vise, bent it and see how it breaks. It shouldn't break just the weld, if it breaks at all then it will take some of the metal plate with it.
Go on www.millerwelders.com and they have some tips on there. Lincoln Welder site has plans for welding tables, etc to build that are nice and some tips on there so check that out too man.