The toilet was not plumbed into a pipe, but just sat over a 4 inch PVC type pipe. 

Put about 2 inches of water through the duplex. 

It was ground down 3 inches and we added 4 new inches of pavement, rolling the pavement, etc. 

As they say, give an inch they will take a mile.

The tenant lived there for 8 years and destroyed every square inch, but it looked perfect on the surface.

The spray foam guy suggests a 1 inch layer on the back of the steel and totally closing up the system.

where it goes up a 1/4 inch and then drops a 1/2 inch is about a 8 foot area.

Stick with 3.5 inch pulls for everything and you'll be fine.

You could add a drop ceiling to all the ceilings of the first-floor apartment to minimize the heat transfer between apartments -- if the ceiling in the basement is high in a 1930-era property I think it's safe to assume 8-foot ceilings throughout which would allow you to drop the ceiling up to six inches with acoustic tiles that also provide great ceiling insulation.

I removed the drywall on 1 side , framed another 2x4 wall up against the original wall , I put in insulation , and hung 2 layers of 1/2 inch drywall on 1 side , and then went to the other side and put up 1 layer of drywall over what was there .