Time to bring this thread to its conclusion... This picture is right after planting:
Seems like most of it worked out as expected. I found the source of the little leak in the bottom tank compartment. Missed to apply epoxy to a small stretch in a corner. Difficult to find, eventually I got a small mirror, connected to a wire, and with a flashlight and that mirror was able to inspect everything.
Since that picture things have been growing nicely. Shrimp and Endlers are alive and well. It has been cold here (down to freezing), and the 150W heater struggles a bit, but overall I am happy with the insulation. I cover the front glass with a sheet of 3/4" styrofoam to prevent heat losses there.
Need to move the heater into the filter chamber, clean the surface which is a bit scummy, and do some final waterproofing on the covers. Need to cover the walls with drywall, and figure out how to lock the top cover to work in the tank. Right now two bungee cords do that, but there must be a better looking way.
Currently I have only 2 of the 4 bulbs running, it is probably time to add a third one, as the plants start to get established.
Anyway, thank you for reading this thread, and special thanks to those that provided feedback and asked questions! Keep asking questions if you should have any, and I will update this thread if anything interesting happens with my new tank.