Random thoughts; I have never been a fan of dimensional lumber. It is frequently loaded with moisture then settles out like bacon.
As a certified hardwood flooring contractor those in our field are aware of the big stability differential between solid wood and engineered wood (plywood) flooring. When we do a floor it must be +/- 3/16" in 10' to be acceptable. I find dimensional benchwork exceeds that.
One of the things that makes Mianne stable is the high quality jig built hard wood used it it's picture frame type of Ikea construction. It's a great idea.
I would never use 2" X 4" table framing. It may work, but, quite possibly there could be problems. The deciding factor for those on the fence is whether or not you are using scale flanges.
Typical 3rail pizza cutter flanges are very forgiving.
Scale flanges and smaller scales (HO-N) need flat surfaces with gentle vertical curves. 2 X 4 construction can warp up something nasty in a few years.
We always use lumber yards which store their plywood or Advantech on flat beds not big box bent steel fingers.
You layout represents the foundation of you whole creation. Give it some love. If you are not sure of how to go about it order the Mianne kit you need. IMO, if you want to up your game, use high quality Birch or Maple 1/2" or 3/4" framing and Advantech decking.
Check out Model Railroad benchwork one of the OGR sponsors who make truly custom benchwork.
One way to assemble a module: