Hive structure is undiggable supports to the greater hives above, or remains of dismantled sections. I't useless and intended as an admittedly fancy looking barrier. I personally like to smooth out and engrave any hive support walls I end up with.
The cultivatorum has "Cultivate Blood Fungii/Waxroot/Cavespore" which yields a from what i can tell 5-7 seeds or something like that of that type. As for the cavespores, think of them as quarry bushes. That cause fevers if you eat them as is. Waxroot can also be pressed into oil should you need it.
I don't think anything besides grox/wild grox will yield a stomach big enough for a bag (represented with them flat not being there.) Your only other options are leather and cloth. And if you find yourself hurting for rope, 3 hearts can be made into a sinew rope, though i don't recall where exactly.
Also, you can make organs edible by applying yeastbath to them. Need some blood fungii, bottled water, and an empty bottle to make it. I'd also recommend making fertilizer (Main post should have the recipe.)
And I'm right there with you on the setting. I feel bad saying that I'm fiddling around with it though (adding a rarish fuel source, improvised protection for hands, stuff like that.) Cause I really don't feel it's my place (I rageed when I finally noticed virtually no basic armor that wasn't easy-to-perforate leather for assault troops aside from scrap body armor, and ranged combat being so heavily emphasized; it's too damn slow in DFs engine, and nowhere near as fun to read.) to do so. But Abregado's been a great sport about it and helped me in some stuff I'm doing for a seperate mod of my own. Seriously man, thanks for putting up with me.
Hope I was helpful Stuebi.