Great feedback here from everyone!
@William Morgan - I think a partnership can be an awesome opportunity for both sides. If you approach your partnership agreement and your subsequent interactions from the perspective of making money AND taking care of the relationship, I think that gives you the best chance of succeeding as a business and ensuring that everyone remains friends.
A few other scenarios to think through: make sure you decide up front what happens if you decide to split up the LLC, but you both want to keep the building. Who would get to buy it from the other person, and at what terms? Better to nail it down now than fight about it later. Also, let's say everything looks good when it's inspected, but there is an unexpected expense up front (like, say, a water pipe freezes this winter and you have to shell out a bunch of money to repair broken water pipe plus add more insulation etc). Who pays for that, your partner? In that case, is that money a capital contribution, or is it a loan? If a loan, in what order is that money paid back (as in, you pay him back the loan first, and then resume payments on your half of the down payment)? Finally, if for some reason something happens and you are forced to sell, in what order is the money paid out? What if there is not enough money to cover the mortgage AND the complete down payment from your partner and whatever you have paid in - who takes the loss? Again, I'm not saying this is likely but these are the kinds of things it is important to think about up front.
And, in addition to working through possible failure scenarios (very important), it's also key to make sure that you plan for success! For example, what if your partnership goes really well, and you decide you want to invest in another property? Would you use the terms in the operating agreement from your existing LLC, or would you plan to structure another one? Not saying you have to figure out the complete framework of another structure up front (that would be premature) - but would be good to think about whether or not this LLC is designed to cover one building, period, and anything else would be a separate conversation, or whether it's designed to expand.
Good luck and keep us posted!