I am planning an extension to my current layout. IN the corner, (least accessible spot) I am going to put a Mt Rushmore there in the corner. I have short arms so I really have to consider REACH.
I am still using the same base layout tables I built over 25yrs ago. I use 1x4 for the frame, long runs aligned with pegboard holes and cross members, also aligned with peg board holes. I cut the overall top shape from a sheet of peg board. I then top that with construction grade (dense) styro foam (painted green) as a base for my layout. I have redone my trackage several times over the decades, but it's still holding up. I PIN the track to the foam, then insert the cork roadbed. I also punch holes, (up from the bottom) straight or angled as needed for wiring.
I recently started doing diorama modules for scenery. I have a small community one, a farm, and a carnival. The Mt Rushmore & a quasi-DC mall will be my next two. The Mr Rushmore in the corner will have another advantage of being easily removed to work on, then just set it back in place.
Track radius; I use old code 80 track, #4 & #6 turnouts, and mainlines are a min 11" , some 9" and a mountain logging area is old Arnold(?) 8"r. I use a good bit of flex track, especially on mains with greater than 11" radius. I also do not like to run my trackage too close to the edges, or back wall.
Modern LONG cars, freight & passenger look better on the larger radi curves. ALL my locos, including my BigBoy & DD40 run w/o problems on 11"r curves, but again look better on wider radi.
TRACK, DC vs DCC. This can be important when laying track. My short mountain oval is DC, and so is my DnTn trolley so far, the later might become another combo section DC/DCC switchable. DCC wiring is far simpler than breaking track into sections for control. Another thing I do different, so it seems, than most, Is NOT all my trackage is connected together. In other words I can not run a train from my mountain, trolley or subway line to the main lines or yard, no need IMO. I also have an oval that is part of my layout that is completely separate (trackage & electrically), DC/DCC switchable, that doubles as a test track oval.
BTW ALL my DCC loco's can run on BOTH DC & DCC. My layout is also broken into segments, such that my subway line is DCC only, no DC trains and runs with a NCE system (that does NOT support DC locos). Everything else DCC is run with Digitrax controllers with works with both DC and DCC locos. DCC is VERY ADDICTIVE. I started with plans to convert just a few locos .... I have well over 100 DCC locos now. Did I mention that DCC is extremely addictive?