Well instead of changing the track height with grades, consider an open grid construction or L-Girder construction. then you can lay the track especially the main on roadbed say 4 inches wide, but have the scenery vary above and below track level quite a bit to create idea of height differences.
I like your track for its implied operation. I have a couple of changes I might consider. First I would move the siding for the warehouse across from the yard to be next to the wall and pull the "passing track" or runaround as near to the other through track as possible. I think having the passing track close to the main will look more realistic. And putting the warehouse against the wall outside the curve will allow the track to be longer and run into the corner. Make the warehouse a low relief flat against the wall with docks and doors modeled. since buildings are so large in O scale, this reduces the footprint and takes advantage of space that might go to waste. also, while you reduce the scenery in the corner at the end of the warehouse track, you could greatly increase it in the other corner. Or you could add a track off the warehouse track back to that other corner for another industry.
I would change the yard ladder a little too. S-curves tend to cause more derailments than straights. I would change the switch to the track next to the yard office from an RH to an LH switch and make the ladder straight. It would give a little more length to those tracks too.
I think I might try to move the engine house track into an area closer to they yard but that may not be very easy.
I just noticed that all of your industries have sidings facing the same ie trailing point as is the yard. I would consider making a couple of them facing the other way, so to switch the cars you have to do a run-around move using the passing track to run around your train to push it the other way into a siding.
Around the walls layouts or layouts against walls are very nice because they let you simulate large structues as flats against the wall and avoid using up valuable real estate for building footprints. The team track/scrap dealer track could also go on the outside of the loop you like.
