When creating an underground Belt or Pipe, it should cost For instance, if I create a 100 length underground Pipe, then it should cost 100 regular Pipes from my inventory. If I do not have 100 in my inventory, then I cannot build it. Same applies to building underground Belts.

That's a completely different approach on fixing the length limit problem and should be its own mod.
And actually, it was: https://mods.factorio.com/mod/Subterrain
I think, I considered using it back then and decided to make my own mod using a much simpler approach instead (yes, this one).
But you could adopt and update it for 2.0.