You will have many electrical headaches because of faulty rail joiners, atlas joiners are not as robust as needed and over time will be dreadful outdoors, soldering jumpers at every connection will be a huge undertaking!!.
If I were to do your RR I'd go dead rail and battery powered RC in locos ,very common in large scale and small enough for O (airwire makes a good system) 1 system in boxcar and power fed to locos will keep costs down.
Elevating tracks will help for maint. and construction.
Have been outside with large scale 5 years, Brass rail and split jaw clamps at every joint. I have had no electrical issues.
You may want to try to put clamps on atlas track I found the center rail will be very tough to do.
Sun( UV )is tough on plastics...I went with minimal structures. Track will suffer over time as well.
Most O diesels have open gears on trucks ...lots of grime and grit outside to get stuck in gears
I'm in PA and found the weather really limits enjoyment on RR...rains on day off ...sunny on work days , I'm not a fan hot weather so more limits.
Not to kill your fun but keep O inside and build robust Large scale outside as even large scale trains appear much smaller outside!! O might get lost!!!
If you want to try it start small and work out the kinks before making huge investments in track.
Good luck, Dave
