To the map:
The river in the mountain is a bit too broad from my point of view. Should be narrower at the source (unless there is a lake or something like that. It just doesn't look like a lake). Generally it looks quiet good.

To the distance: I think a horse can't go much further than a man can go (especially with the backpack) it just moves faster (but needs a brake every now and then). I have to talk with my sister in law about this, she's riding horses since she was 7 so she should know.