Lights?. Once you've run lit passenger cars at night you won't care anymore
Tin Marx? 4" cars? 6"? Postwar plastic? 2 axle or four? etc. (Marx made a lot of stuff pre-60s)
Gathering a list of items you have may help inspire design and speed answers. From buildings to power supplies on hand. It can get frustrating always asking which, what, where, etc. when helping others.... "delay of game... three day penalty while the helper is busy with life". Marty F. used to "looze it" from asking the same questions three times daily, six days a week. Better too much info than too little
If you run Windows try the trial version of SCARM (capable,3d) and/or Anyrail softwares. Getting a head start helps you be more involved and takes some pressure off the helper.too.
200lbs ? In the corner maybe. Climbing onto it isn't the same as staying there. That much stone could warp a length pretty fast imo. Adding extra bracing and legs there would be smart if you haven't followed a "cabinet makers design" of some kind.
I'd have to see the stone, but faux finishes aren't real hard. Plastic wrap as a "stamp" of sorts creates random 2-3 tone mineral lines well. Buried in clear it becomes "polished stone". "As beautiful?" I've been faked by faux stone, and I've done it pro too; so....maybe (Turning stuff into mahogany was funnest)
The end result is often partially luck. Usually, the less I really try; the better it usually looked, as nature likes to be random too.
At 1:48 scale a marble detail is hard to do, but I've seen decent.
You might also want to peek at Thor's website for Marx and toy soldiers for ideas (Thor has passed, but the site was still up last I looked. Best to not delay and miss this little jewel. His toy sites all had links to his others somewhere, so if you find one, might as well browse some there then link when you find one.
Search threads by "Electroliner" I really liked his stuff. (New home fire took it, then he passed...of a broken heart most likely )