Yes 10ft is cool but the section is imho too small. I have seen individuals reaching nearly 20 cm in length and they are very fast and active swimmers. So 40x40cm is imho a little too small. I would at least go for 60x60cm.
Does that heater not have a "Do not submerse past this line" marking on it?
Nice job by the way, I look forward to seeing the tank once you're done filling it, and again in a year once the plants have filled in.
Mine is a Jager as well, but mine says this...
View attachment 81777
Which I understand means "Keep this part out of the water."
I suppose yours does look a bit different than mine though, so could be a fully subresible unit.