@Laura Costello Good question! It depends, sounds like this friend is going to be relatively passive in the project, more like a private equity partner. In my current deal, I'm setting up a similar scenario, borrowing $150-200k. The terms I arrange with my partner was not profit-sharing, but just 10%APR. On a short term investment (~4-6mo) he can make $7-10k for doing nothing but lending me the money. That to say, you could structure it differently than profit sharing, don't assume that you'll need to give that much away to borrow their money. They can make 10% in the stock market right now, but that may not last, and its they have no knowledge/control advantage, so in essence your providing a safer investment with better terms. IF I were to set up profit sharing for a private equity partner, I don't think I'd be inclined to do any more than 25% but it will totally depend on what they need to make it work.
That said, all my thoughts are moot if they want a more active role. Then you would want a formally drafted agreement outlining percentages of capital input, workload and profit/loss splits. Good luck!