Hello ! i'm playing WW barb a lot, i'll try to answer.
1. It regens wrath passively, and you gain movespeed compared to LR/Slanderer, but it looks like LR/Slander deals way more dmg, better for pushing. Bul khatos better for speed farming.
2. Ground stomp is here to procc The toughness bonus from band of might, and also pack many mobs on the same spot.
Sprint build probably for speedfarm.
Don't really know, maybe player preferences, personally, i use warcry - veteran's warning. better survivability
3. Bovine Bardiche opens cow levels in the cube, as u do with the puzle ring. Btw ancient puzzle rings will open an ancient vault flooded by Gobs.
Stone of jordan is kinda good too for WW T16, crushing elites easily.
4. You will need Focus and restraint on your char (for high grs its way more efficient than COE), use obsidian and band of might in the cube with ambo's pride.
You can still use COE for normal rifts but i prefer stone of jordan.
Try getting a flavor of time by upgrading rares in the cube maybe.
Put yourself an own goal, like clearing 110 GR or higher.