Sorry to be coming in on this thread so late. This design looks great. If you're worried about access to set up stock or deal with any potential derailment at the back, you could consider moving the back scene divider forward about 8" and making approximately the last 2' of the scene divider oblique on each end, maybe backward on the right and forward on the left.
This would leave room for a modest sized access well maybe 18"x2' behind the divider approximately in squares 2,3,8,9 of the middle row and some of the squares behind. You could consider raising the level of the baseboard to provide easier access to the wells and potentially you would be looking "at the trains" rather than down upon them. You could set up stock or deal with issues from the wells.
I'm assuming the the back of the layout would be against the wall hence concerns over access. With this arrangement, I think this would appeal visually if you entered the room or whatever from the right, mirror image the suggested design if there is a door on the left. The back scene divider would now be almost 12 feet long.
There is quite a lot of spare room on the left side if the divider is brought 'forward' in this way. Trains enter/leave via a tunnel. The storage sidings on the inside become progressively shorter but could be extended into this area on the left to accommodate longer trains by replacing maybe two of the left-hand turnouts with single-slips. The last couple of coaches would need to be reversed into the additional area for running in a clockwise direction. This could all occur behind the back scene.
If you can squeeze another 4-6" in depth there is an option to have two running loops of the same radius as this as you have just sufficient length for an elevated track with no more than a 3% gradient. The tracks partially overlap (one elevated) behind the back scene.
I don't have a planner like Glenderg or Dave but I can PM you a sketch if/when you're interesting in moving ahead.