Great photo journal. I'll keep an eye on your progress . Thanks for explaining what you're doing.

I usually put some aquarium silicone (just a few lines) on the back of the tank before I spray the foam. I also don't believe in layering it - it will have better cohesion if it all cures together. Curing takes a long time though if it's a thick layer, which is a downside.

I think you'll regret not having a drainage layer. The substrate will become anaerobic, won't support so many micro organisms, and it will likely be somewhat more smelly than it should be.