A manual turntable is relatively easy to construct. Get your router out and fashion an extension to the base ("router on a stick") to cut large circles in plywood. Pay attention to keeping the pivot point in the pit centered on the rim of the pit when assembling.
The automation of the turntable with indexing is an interesting challenge - Arduino, steppers, motors, fine positioning, locking in position, etc. makes a nice project. Remember that scale locos have scale weights that impose loads on the motors that stall rotation. (I have observed that stalling the drive mechanism IS prototypical.)
The manual turntable uses the ever reliable arm-strong motor and Mk. I eyeball for positioning, and, for my DIY turntable used in modular shows, works very well with virtually no training needed for the operators.
The wiring of the bridge track implies a slip ring or an overhead wire. My quick hack of letting a twisted wire pair hang underneath has survived a couple of decades with o need to re-engineer the solution. Adding a motor (and the temptation for continuous rotation) would require slip rings or an overhead power feed.
Wiring storage tracks and a switch panel is tedious. and if I repeat the process, I may go with an LCS BPC.
I recommend you build a manual turntable first.
