Let me get this straight. You have an idea to open a shop and not some small time stuff. Stuff that will take big bucks and you automatically think it will work.
I'm not trying to be negative but lets get real. You are very young no one will be willing to risk all their money while you lose nothing. It has to be a win-win situation.
Also you plan to buy out your partner? If the business starts doing really well that won't be fair at all.
Also there are numerous shops that already have settled themself. Just because you love talking about cars all the time does not mean you will know what to do. Have you ever gotten dirty and rebuilt an engine or tranny? Ever rebuilt a whole car? Do you have any mechincal knowledge and have you worked for anywhere?
I mean I am pretty sure I around your age, but these are ideas I had when I was younger and into that whole Import Tuning stuff.
I mean keep going for it but be realistic and realize some stuff. Also you stated you made 100k off ebay? Where is that money then? 100k is a lot of money especially at 14 where is that cash?