It is very hard to get an exchange up with just 10BTC. I am thinking around 100BTC will be a more reasonable number. If you think you can get it done with 10BTC then it is really great.

Instead of talking about how you could pay back the loan, try to show what you can do. Your skill, experience and past work will go a long way to convince me to send you money. I may even want to become partner and fund the whole thing if I believe you can full it off.