I went down to the garage and looked at mine, and it's a 6.5 hp with cast iron pump. Sticker says it will deliver 10.3 cfm @ 90 psi, which is nearly double what the VT6300 will do. I looked around a little on the net, and is it just me, or have these things really went up in price over the last few years? It's all Bayou's fault for promoting that class action suit!
The breaker thing is a piece of cake, Khamburg. My house was built in 69, and also has the box in the garage. Just shut off the main, and don't touch any wires going to it. All the smaller breakers should be below the main. You will have to remove the panel that covers them. You need to note the brand of the box. Mine is a Square D.
Lowe's or Home Depot will have everything you need, even the conduit to run the wire through. I was able to make mine look exactly like the other outlets and switches in the garage. Mine are all metal since there is no sheetrock down there.
If you have any doubt about being able to do it safely yourself, by all means get an electrician. I wouldn't think it would cost all that much.