This post shows the clusters (this may be in other places too but this is where I found it)
WoW Classic Era Realm Connections Coming May 18 - WoW Classic / WoW Classic General Discussion - World of Warcraft Forums (blizzard.com)
Bloodsail Buccaneers is where people are doing hardcore. Since it’s labeled RP it’s not in a cluster.
The Whitemane cluster is the main PVP option and that’s what you should play on. Yes just make the toon on Whitemane that’s easiest.