Loans have intrest rates that "create additional value". Given the limited amount of bitcoins, couldn't we realistically run out of them?
No, you wouldn't run out of Bitcoins for the simple fact that they will always be traded. Your interest payments on your loan would come out of Bitcoin trading that you did to increase your Bitcoins, even if you only did Bitcoin trading to repay your loan.
If ALL Bitcoin holders became hoarders, the price of Bitcoins would increase as more and more people wanted some. Bitcoin, if as rare as gold and jewels, becomes more valuable. Finally, when the "price" of Bitcoins was high enough, some hoarders would trade theirs off for fiat currencies, just like gold and silver.
People or companies who loan Bitcoin need to be as careful as those who borrow them. If a lender lends when the Bitcoin price is high, and then the Bitcoin price drops, it will be much more easier for the borrower to "purchase" more bitcoins to pay off the loan. This may be adverse to the lender's financial plan.
On the other hand, if the borrower borrows when the price is low, and then the price goes way up, the borrower might be scrambling just to make payments so that he doesn't lose the house, and his proverbial shirt.
As Bitcoin becomes more commonplace, there might come into being "holding houses" that hold the paper on property that secures the loans that lenders make.