a couple of thoughts;
First, turn outs will be the cause of most of your operating problems, but you want to have sidings and make sure a train can pass from one loop to another, so they are needed. I would consider something other than the old Lionel 022 switches. I have them on my layout, and trains will got through them, but not real smooth. I'd consider the ross tinplate, or some have used the K-Line snap track turnouts with good. results. If you are using Lionel's, make sure you can easily reach all those turnouts.
Second, you seem to have one extra pair of turnouts. See my edit to your plan. Trains will still be able to move back and forth from the inner and outer loops with two less.
Third, I would consider a wider radius for your outside loop. If the inner is 31", look to 42" curves on the other, even small postwar locos look much better coming around these curves.
For the blocks, generally I make blocks on all my sidings, but yours are kind of short, so I don't know if you can have a loco and cars and still fit on the sidings. But if you want to, I make the block just after the turnout. I'd also make a separate blocks for the two route options on the outer route. You can park a train by turning the particular block off.
Just my 2 cents. But I run all post and prewar, and this has been my experience through three layouts. Good luck, post pictures when you build!
Tim
