If your thinking of geese instead of turkey I would suggest making sure you like the flavor and texture. Goose is different from turkey just as turkey is different from chicken. Some love it, others not as much. Goose is usually available in the freezer sections of grocery stores at least where I live.
Geese are awesome at mowing the grass. 8 acres is big enough for a lot of geese but your right about the water needs. They can mess up water pretty fast but that water can go back to the grass which they eat so depending on how you do it its not necessarily a waste. I move several kiddie pools around and my front yard stays green and the side field stays fairly green. I use the water from their pens in summer to water blueberries and flowers. I use collected rain water as much as I can. I live in Oregon so I get plenty of rain lol. Basically I have little expense on their water but more work. Kind of depends on your set up but its doable.
Uhh turkeys... I have never had them. Neighbors tried having them, and we have wild turkeys here so I am familiar with them to some extent. The neighbors turkeys turned mean and started attacking everyone. They were scared of dealing with them and I can't blame them. I ended up butchering and got half. I have heard (from several different people) that they can be as sweet as can be till they get older then turn mean. I think it would depend on the same things as with geese. Hormones, gender, how kindly they are treated, how well you can assert yourself when needed, etc. I see them as much the same in temperament at least with the ones I have dealt with. Geese are messier though and need more water.