My family I know had a wedding in the family yesterday... wanted to have the wedding on the farm.  As I understand, they opened up the pasture, and had the ceremony in the pasture.  Took a portion of the hay field aside the pasture... killed it down last fall, and planted lawn grass.  This spring they started the mowing and it made it nice.... used the newly-seeded lawn to put up a (rented) tent, and for parking.  This is an active working dairy farm.  Flies are not a problem yet, and this location on the farm was far enough from the buildings that flies were not a problem.

Another farm family that I know... a couple years ago, their daughter wanted a wedding on the farm.  Again, rented a tent and put it up in the yard.  This farm did not have livestock on the farm, so flies were not an issue.

I am aware of a family nearby who used to have a dairy farm.  They sold the cows and turned the farm into an event center.  This would have the look of an farm wedding, but the facilities would be more prepared to host the public.  Not sure what they charge.

Just thought I would share these ideas, if any are of value.