That is quite the layout you have there. I have never seen that type of pipe before, but it looks like it has rubber seals or is it glued together? Have you found any problems with the ground not being 100% level?
Masu, with such a long NFT run, will there be any food left for the end plants? I guess you have a sump in there somewhere? Nice job drilling all those holes. Hope to see what happens next with the plants and fish. And the DWC is very deep. Canopy for the fish to chew on?
Keep an eye on the roots, if they grow very long the pipe will fill up with them and block the water way and drain a tank overnight.
Are those fish speckled trout?
OK, I now see the sump cut out in post 4 photo.
As far a the level, I would survey it and plant stakes. Did you do that or eyeball it. The flow in the pipes will show how well you did that's for sure.