@Fireball RR Fireball - check out my Twin Pines RR layout. It fits into a 10x13 space. Only the outer loop has 072 plus diameter curves. The rest is minimum 042 (except in a couple of yard areas where only freight cars are backed in.
No way you can get a walk in with 072 curves - you need a minimum of 18 feet - and you will have large inaccessible areas at either end. You would need pop ups in the middle of the curves.
@Tom Tee is a guru when it comes to railroading. The only addition I would make is: there is a huge difference in space requirements for 2 rail scale and 3 rail high rail. Because of compromises made with the build of high rail engines, this version of O gauge requires 1/2 the track space of 2 rail. This is where the discussion sometimes goes off the rails - I have the new MTH Big Boy which can run on my "tiny" layout through the 072 diameter curves. However this engine overhangs the track by several inches going thru the curves so it really does not "look good" in so doing. To me I really like the performance and look of the engine, so while I do not care for the overhang, I choose to ignore it. I have sold off nearly all my semi-scale equipment preferring scale engines and freight cars - because I thought they did not "look right" on my tiny layout. Contradiction? - maybe - go figure, I'll have to just shrug my shoulders on this one - I like what I like. You get to do what you like and looks right to you, no one else's opinion really matters.
Other observations:
Your space is 3 feet wider than mine in perspective - I would love the extra room but it really would not let me do a whole lot different except add a double main line. The extra 3 feet does allow you to change elevation a little more and keep grades no more than 3%
I tried working in mountains, I just did not think they looked right so pushed them into the backgrounds.
Try to work in 3 to 6 inches of space between track edge and walls - more being better. It gives you room to put in details. I had to remove my background mountain because the BigBoy crashed into it going around a curve. Just a 3 inch long section is a problem by no more than 1/2 inch in thickness, so I have to do some surgery on the mountain.
I would not give up on the big curves - personal preference - I gave up a walk in (045 Atlas curves) for the 072 curves because they were more important. I substituted swing outs and lift outs to get into my interior space. I prefer to run outside the layout - i don't like spinning around like a top watching the trains run around in a circle from inside - I get dizzy. Grandkids on the other hand love it - standing in the middle dancing around.
The things you learn by doing. Happy RailRoading!