Welcome to the forums and the server! If you’re looking for Horde guilds, a great place to start is the guild directory.
I’m not as familiar with guilds that do an even mixture of RP, PvP, and PvE. Most tend to focus on just one aspect. Like in my guild. Sure we have a mythic+ group and will help one another out with PvE, but a good 95% of our collective guild time in game is spent RP’ing.