@Matt Friesz there is no right answer here. It's all negotiable, and whatever the two of you come to; hopefully you both feel like winners.
I may be a minority here with this view, but I'd be hesitant to make any binding/long-term relationship. It means that you are more obligated to him and going off on your own will be more difficult in the future. Instead, you can have a general understanding of what you're both trying to do, and then as deals come along, you jv/partner for each one.
For example, let's say he wants to go 50/50. But what if in 6 months, you find someone who wants to "join" you, and all he needs is 8-12% annually. He doesn't care about upside. If you have a real partnership with Mr. Money Bags over there, this new Piggy Bank is of little benefit to you, and you're still locked into giving MMB half of every deal.
As a general negotiating item, the more of a preferred return you can offer him, the more equity you should be able to keep. Or if you give him no preferred return, he's going to likely demand more of the deal.
Lastly, the key to this business is building equity, not cashflow. Cashflow is really important for a bunch of reasons, but wealth is in the equity - keep as much of it as you can, even if it means giving a higher pref and making less money in the now.