Hey hey person! I can see you’re playing the best race in the game so let me jump right in and help with some of your questions.
Org and Stormwind are the “Main” ones, however there are many useful pockets of RP being kept going by guilds and communities. Some off the top of my head are Feralas (Night Elves), Azshara (Horde), Silvermoon (Horde Elves) and Lordaeron (Loyalists, Scarlets, Ebons).
Did you know the best PCU guild, dare I say best guild on AD, is a Nightborne guild [PCU] Eternal Sisterhood - The Guild Formerly Known as Moonlight Melody 
check us out. We’re the centre of all the zany on this server and have something for everyone. Although we do specialise in Cult fanaticism, Highborne aesthetic and being mildly lawful evil