Hi:
I’d take the crossovers off the back of the layout and move them to the front. Blend the transitions into the curves at each end using a pair of turnouts. If the square in your grid in the lower left corner is “0,0” then a turnout in the inner loop at 3,4 with it’s straight section pointing towards the outer loop and a turnout on the outer loop somewhere around 4,2 with it’s curve pointing towards the inner loop might work. Mirror this at the right side of the layout.
This would allow you to start elevating the outer loop at square 4,2 and by the time you got to the back, at 8,8, you could have some decent height to work with for your scenery. I can see a nice 6’-0” long trestle running across the back of your layout. It takes a lot of length to raise an “O” gauge track 6-7 inches.
You might want to flip the siding at the front, between squares 7,3 and 16,3, to the outside of the outer loop to simplify the turnout situation at each end.
Boy, you sure are luck to have so much space! Have fun with it!
Regards,
Ted