Here is another, more basic, free area planner:
http://print-graph-paper.com/virtual-graph-paper
I would have a hard time planning where I lose the whole length aisle, unless one end you can’t exit easily anyway, like there is a drop-off and no way to drive out and around thru there, or a perimeter fence that can’t be changed, or such.
40’ long and so is very small and that whole length aisle seems a waste of space, but still …
Maybe having two exits in the barn is not that important for airflow and traffic thru it where you are.
The barns like that I have seen could have used that other door, if nothing else for ventilation.
One had a big fan on that end where the aisle would end, but it was way not enough, air in the stalls still felt stale.
I wonder if fixing that barn where it can be expanded in length soon for those extra stalls and storage space would not make sense, since that is really crowding things in there to get it all in the current space.
As for an indoor wash stall, you don’t need a drain on the floor.
Many do fine with letting water out of the back into a little French drain of rocks.
Ours has held wonderfully to lots of traffic washing horses and tack.