I work in the grain marketing / risk management / Financial analysis business with farmers and also help a friend farm. I have worked with some guys in the past that would be in your shoes. Here is my 2 cents.......and it might not be worth that.
By the original post it appears that you have helped on the farm but don't really know a lot about the business end of farming. If you are going to get in to a crop share arrangement then I would highly advise to either go with the guy who is a family friend or you can trust or have someone who knows farming to back you up and help you get your feet wet. Whether it is a friend / family member who is farming or an adviser you pay something to help, this can be crucial.
I am working with someone now who lives on the east coast but decided to buy ground and go crop share with a farmer in the area. He went up and looked at the farm 2-3 times per year and and thought he knew what he was doing. The crop share farmer kept telling him he figured the corn would go 160 bu/acre so not knowing any better he went out and sold 160 bu/acre at $4-5 / bushel. It yielded 109 and the market went up to $6-7 / bushel and he was forced to buy $6-7 corn to offset the corn he sold for $4-5. Someone who knows what they're doing knows the most you sell is your crop insurance guaranteed bushels and no more until you know how many bushels you have. He didn't know that and it cost him a bunch.
The crop share tenant also decided combine all his crop share ground first way too early at 28-29% moisture. Hauled it to his own drying setup and charged the landowner drying that was commercial elevator drying rates or even a little higher and shrunk his corn bushels 2% / point removed. So if he had 100 bushels at 28% after the tenant got done with him he had 74 bushels at 15% after shrink was taken. If you know what you're doing drying corn shrink should be 1.18% shrink which is taking only the water out. Most elevators are 1.35%-1.45% shrink per point and they are always long bushels the end of the year. So in the end, the landowner had 2,500 bushels less to sell because the tenant screwed him over. The tenant also got to sell 2,500 bushels more because essentially he stole the bushels from the land owner. Until he had me look over stuff he had no clue what was happening to him.
I am not trying to scare you out of doing it because I hope to have the opportunity to have control over land my grandfather farmed. I just want to make sure you have someone who knows the business help you get your feet wet so in case you get one of the tenants like the one in the example above, you can stop it before it's done.