Many of your suggestions have already been made, whether we’ll see them added to the game only the devs know.
Have you tried clicking on a section of road and then upgrading it that way?
Devs so far have avoided New World crops like potatoes, corn, etc, though they haven’t ruled out the possibility of adding them in the future.
As far as diseases go count yourself lucky.
All Them Old-Timey Diseases - Farthest Frontier / Dev Discussions - Crate Entertainment Forum