What kind of friend is this?
Long time childhood friend or work friend, neighbor friend, ect.... It makes a difference.
Then the next thing would be... Is the possible profit from this joint venture worth possibly losing that friend?
It does not have to come to that but it may and you need to know how this "friend" ranks in your book.
After that yall need to sit down and talk out exactly how this is going to be ran. Are yall going in as equal partners, is he a silent partner, is he soley and investor. Basically you got to know in the end who makes the call.
I would be weary of equal partnerships but if it is actually possible for that person to invest and let you make the final calls then it could be a good deal.
Last of all,,, after yall have figured out where every one stands,,, put it in writing. Make up basically a contract that says every thing yall have decided on. That away every thing is done according to how it was stated by both parties or there will be penalties. IF you make the calls.... he is just an investor... and he startes pushing his way in trying to make calls you want the contract to cover you so you can get out with your fair share and/ or compensation.