Congrats on getting space. Two years ago I was running multi-gauge on my 9 by 9 layout. I joined a club and got to build out on a 8 by 10 table. This past October they allowed me to expand it out another 9ft into another room.
To quote Spock from Star Trek 2 "His pattern indicates 2 dimensional thinking." I encourage you to think and design in three dimensions. Build up as well as out. This video starts out in the new addition which I am still working on. I can run 8 trains at the same time. I have 2 multi-gauge tracks that can run O or Standard. I have 3 tracks that are Standard only and 3 tracks that are O-Gauge only.