Maybe the dimensions are where Hagoromo got the idea from. Or since kaguya was always the will of the juubi and Hagoromo sealed it, had something to deal with the connection between them after he split them apart. Each representings its own.It could be possible but I don't unterstand the reference of the Bijuu and Kaguya as they were created much later on.
I doubt shukaku has sand. Its just Gaara that can use sand, just like his father and probably other kazakages. Shukaku's forte is sealing, thats what Naruto needed from him.
Kurama can absorb nature energy,
We could see he can use Lava after he called upon goku
We saw Naruto can use boil release after he called upon Kukou.
And thats why I think all shukaku can help naruto with is sealing techniques.
But yeah, I think kishi is just running out of ideas so he just uses some of the tailed beast's elements hahah
Maybe I should reword this , they were made from component from these dimensions .