Just off the top of my head... Never really did anything but these can be the bare basics...
- Go to automotive school possibly take some business course or class to get a grasp of how things would run
- Save, save, save and save your money and be sure you two trust each other and that nothing will get in the way of the business between you two
- Location is another thing to consider
- If you want to be a vendor start out in a warehouse/garage type of layout so when you are ready you can get setup for an automotive shop with enough room to move around and work
- What type of shop would it be? Domestic, Euro, Tuner or Everything?
- Build yourself up as a vendor first then get it out there that you are opening up a performance shop
- Build a clientele through being a vendor for locals if you have regulars offer them a reduced rate install prices in your shop have them get your name out there through your work and quality service
It's definitely a timely process that goes into it but I'm sure if it's quality stuff and work you'd be doing fine. Unless you're working while in school you'll need to get a job after it save your money and when the time is right begin the process. Well to think about it depending on how you live you probably would still need to work some more and save. But I think you may be able to do small business loans through banks but would need some sort of collateral etc etc.
Then again I don't know details and never did such a thing but I'm just throwing ideas of what would be somewhat reasonable IMO. Maybe that gives you an idea though...