Ditto on Si's Left-Handed switch.
Sharp and without a section to straighten trains (at least one full car length) in S curves cause derailments.
Your second plan looks better.
Spray insulation is great.
Make sure that you tape of ALL track. You can't undo that stuff when it gets on the track, don't ask how I know.
I use a combination of blue or pink styrofoam insulation board with the spray foam.
It builds up rapidly that way.
Once dry all of it shapes with a serrated knife and a rasp.
Then I coat over with inexpensive drywall joint compound with a little bit of paint mixed in (for chipping insurance).
You can use the boards for your dividers too,
just paint a white primer over them,
then you can paint whatever you want on them.
____________________ Steven B.
Humboldt & Toiyabe Rwy