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 2 turntables in a small layout?  Seems like using a lot of real estate for that?

Remember that when you do an S curve, you need a straight area between the 2.  Said area should be as long as the longest car you intend to un thru there.

Does the car float have anywhere to go to?

2 turntables

Yes, two turntables, maybe overdoing it, but I found that doodlebugs cannot run backwards, and also that I could turn helpers.

Yes, S curves, I'm aware of that, but where did you spot them? 40' and 50' cars, maybe longer passenger cars. Thanks for the heads-up.

Grades

 As far as I can tell, your grades are going to be very daunting (I would use the term "horrible" but i'm trying to be positive).    It looks like you have an almost 9 in elevation change in about 16 ft, that's over a 4% grade.  With your era you are probably talking about steam.  Sharp curves, steep grades, small steam engines, not the best combination.

tough grades

Yes, grades will be tough, but I will give it try. In case it turns out that the grades are too steep for my engines I will have to rethink, but … until then I'll put my head in the sand .

(Steam or diesel, double heading or helper.)

 "two turntables, maybe

on small layouts it's handy to use one turntable and yard to represent both ends of the modeled run. A route that goes from a yard, twice around the room,and to the opposite end of the same yard works well. A carfloat operation is also a good way to model interesting operations in a small space.Mark Dance's N scale version would work very well as a stand alone HO layout in a room your size .....DaveB 

The grade check is likely

The grade check is likely your first failure point on the design. If you use thinner bench work and limit the difference rail head to rail head to 6 inches maximum you can reduce your grade % from approximately 4.5% to just about 3%. Even with that it is steep and you would likely be looking at shays, and saddle tank engines to move very short trains. Early diesels like box cabs were also used in environments such as this.

Two turn tables would also be a large waste of resources for the distances involved. Unless you already have two I would limit it to one on the top level and place the second on the lower level at the Ikea shelves and use it to turn locomotives going up the grades. One thing that might help is the fact that you could use the continuous running feature of the lower level to build up speed and get a run for the hill. If you don't already have the second turntable a wye track could be used to turn locomotives and it could be located on top of the lower level Ikea shelves.

Your era is 1948 to 1950 so small steam or even GP7s or even SD7s or similar diesels could be used GP7s 1949 intro. Also early sw or alco switchers could be used RS1s even early FMs. If diesels are used you only need to run around the train on the lower level and they will pul the grades better than steam engines in model form. Other than the grade check and what might be too many turn tables the layout looks very interesting to me and would likely be a ton of fun for one or two guys.

I suspect your first draft was very close to success.

s curves

 Near the one turntable, but mostly I see them with crossover switches, where you are going from 1 curve to the other with no straight between.  It might work, but it also might cause derailments.