My feeling is that you almost can't have too much land.

When I was growing up, we had 55 acres and that provided enough room to do anything we wanted from a "hobby farm" perspective (animals plus agriculture, outbuildings, etc). We kept about 10 acres of it mowed in various degrees of finish (some fields, some lawn, etc). Even with that much land, you'll notice the neighbors... and probably want to do something (like plant a tree line) to seclude yourself.

Later on, we got a five-acre piece with only about 1.5 acres mowed and the rest were heavily wooded. This attracted a lot more bugs, but the seclusion was nice. Not as much room to roam but still enough to let some animals out. They really don't need a whole lot of room to be "free range" ... sheep can easily get by on an acre, and chickens need much less.

As a general guideline, you could get by with as little as five acres, but I'd recommend going for 20+... and if it's cheap, the more the merrier.Tthen you can have things like riding trails, maybe a pond, some varying topography (if such a thing exists in the midwest!), an the freedom to do whatever strikes your fancy over the next 10-30 years (or however long you live there).

I think one of the main reasons people live in the country is so that they can stay off the grid and not have to rely on the city for things like water and sewer. When I evaluate a place in the country, if it doesn't have its own well and septic, it's much less desirable. Right now I live in the city and between home and work we spend ~$200/month on bottled water because I would never drink the processed city water. So without a doubt, you want a place with a good well.