Take your time with the axle setup, and get your tolerances right. If you have any questions about shims and spacing, make a thread and post it up. You need some kind of gear marking compound (my kit had some bright yellow grease) so you can see how the gears mesh. The pattern needs to be right. You probably already know that, but make sure you don't take any short cuts dealing with the axle.
Dude, that welder is bad to the bone! I am jealous.
I have a CH 105A Mig for sheet metal and a Miller Thunderbolt 230A for stick. Clay bought a Lincoln 180C Mig and it is very impressive. He is wanting a TIG now.
Hope he gets one... I want to build a boat! I graduated from college with an Ag degree, double major in Animal Science and Industrial Technology. Both majors served me well, and I enjoyed agriculture (still do!), but I am not working in my field these past three years. The industrial portion provided TONS of experience to do a lot of different things over the years. I think you have a good concept and you have an excellent start. If you REALLY LIKE agriculture, and you want to use your hands, look seriously into Ag Engineering. It's a great occupation, busy, and good paying.