I don't understand your point about paths. They have no effect right now, so why show them?
The paths are present on the ground in large numbers, so should be in the game. The same goes for any more piles of useless (at first sight) objects - boats, benches, fences, haystacks, etc. It is certainly possible to do, but then lost some realism.
Splitting infantry from their vehicles - I didn't know we could do it. I will try it out!
Select all squads what you need, right click on platoon icon (on quick selection tab) then in popup menu deselect those groups that you do not need (such as APC, if you want to use only the infantry). To avoid to repeat it every time, save the selection to the group (Ctrl+Number).
In general, the in-game assistant tells it all