I don't want to be that guy that says: I told you, but...
I think this is a good ideea, and i would invest in it, but the business plan is wrong.
"(4) The price goes down fast, we may lose some money. "
This is not how arbitrage it's done. This risk should not exist. You don't have to wait for the funds to transfer between accounts. You must have funds available on bouth, or more exchanges and the secound you sel on one exchange you buy on another and you make a profit. Regardless on the price change, this should not affect you. And you must use the money so you do the arbitrage each day, transfer every day, not wait for the rounds.
You should substitute with:
(4) The Bitcoin Arbitrage Fund disapears with all the investors money.
or better make it risk number 1, because if you don't know how arbitrage is done but you start a Fund... this is really the only risk for the investors.