Things I would recommend looking at:
1. Flood maps and how well it drains. If you can go take a look at it after a heavy rain, you'll see what the overall area looks like, roads, drainage, ditches, etc.
2. Condition of well pump, depth of well, etc. Should be able to get that info from the current owner. Find out if you can what type of pipe was used for distribution.
3. Condition of fences. Fences are maintenance and expensive.
4. Any equipment that will convey with the house - you'll need a tractor for sure on 20 acres. Tractors aren't cheap, if one conveys, all the better assuming it is decent or better condition.
5. Neighbors, neighbors, neighbors. Drive around the area and look at your neighbors as well. Nothing can make life more miserable than a butthole neighbor that doesn't keep their place up, etc.
6. Traffic. Go during morning and evening rush hour. May find that it takes a lot longer to get home or get to the shipyard than you think because of traffic.
7. Condition of roads...says a lot about how the county works in that area. Sounds dumb, but having a county commissioner or government that is responsive is a huge perk, especially when it comes to maintenance, drainage, etc.
8. Power lines and trees - losing power sucks. ARe the power poles old, leaning, not well maintained or do they look pretty solid?