How are you planning to hedge against a heavy fall in the BTC/EUR rate? I'm not aware of any cheap high-volume means to do so (other than converting into fiat which would be rather pointless).
Your plan pretty much relies on BTC rising vs EUR. Whilst I'd tend to agree that long-term that seems likely it's also likely that any such rise won't be a steady one but will have the occasional large bubble + collapse.
If BTC happens to be at the top of a bubble when you launch it could be rather a problem for you. Whilst you may hope your own purchases could extend the bubble you can't really base a whole business plan on hoping BTC doesn't have a collapse shortly after you start taking deposits (if it happens later then it isn't such a big problem - after a while only a total collapse of BTC would be a major issue for you).
It's certainly an interesting business model - borrow money denominated in EUR then bet it all on BTC rising. And rather than paying interest for the loans to speculate with, charge them fees for the privilege.
We shall be operating our own local index based on several determining factors to prevent bubbles having a detrimental effect on our operations, these bubbles will also provide us with the opportunity to strengthen our own position.
How does having your own local index protect against exchange-rate movement?
Customer deposits Euro and wants a Euro-denominated account. You can't use a local index to change how many Euros he deposits.
You then purchase BTC. It doesn't matter what your index says, you have to buy them at market rate from someone selling them.
BTC then crashes vs Euro.
How does your index protect against that?
I can see your own index helping you when people deposit Euros and want a BTC-denominated account, but by your own estimates 98% of accounts will be Euro-denominated. The 2% that are BTC-denominated can't provide useful hedging for the other 98% of customers no matter what your index says.