Long time White Scars fan + player here, played them alot in 5th and am slowly returning to 40k with 9th edition. I think I've loved them since I was introduced to them in Index Astartes in WD140.
Anyway, I bought the White Scars supplement and thought I'd try something else than what seems to be the go-to WS units - Bladeguard, assault intercessors, Kor'sarro etc. I got a strong feel for the fifth brotherhood, which focuses on Stormseers, Vanguard (assuming this means the Phobos units) and generally *hitting a target with everything at once*.
So I thought I'd base the army around two Phobos Librarians and try to utilize their powers as much as possible. One using Temporal Corridor and Tenebrous Curse, one using Blasting Gale/Ride the Winds/Storm-wreathed. I like the idea of crowd control, mass medium range shooting, before moving in and finishing them off - standard mongol procedure, if you will. I got one lib, 2x5 assault bolter intercessors and 3 outriders so far and am pretty set for 6 plasma inceptors, the rest is up for discussion.