Have you seen this page? Some helpful hints there about smoothing out the flat parts to the hill parts.
http://cownap.com/~mtmg/traxx/altitude.html
I like the lake in the corner to prevent anybody cutting across for a short cut. Hills work well in the same way.
Start / finish line can be anywhere. It's always nice to have a bit of a straight stretch just before the finish so you have a chance to race it out.
Since you're using farmroad then trees and a barn and a few cows are always fun. If you check Mal's page, you might like some of the evo conversion models.