Hello, friend!
I tend to find joining, or at the very least reaching out to guilds, is a good way to find yourself some RP or find where the RP “hotspots” are. If you’re looking to make some Demon Hunter friends, Veiled Glaive immediately spring to mind:
https://www.argentarchives.org/node/235061
If you’re still angry about Teldrassil and want to let rip on some Horde, the Dirge of Teldrassil might be what you’re looking for.
I am sure that there will be more that people will pop up with. Welcome back, by the way!
As for the topic, I find that there’s some odd combos that have gotten people the side-eye before but if you’re willing to put in a bit of work to have an explanation on hand I’ve never found it to be an issue. Wowpedia is usually pretty good with this so maybe spend a little time reading up on Demon Hunters, what happened in Legion since you’ll probably blow through it while levelling and there was a fair amount of Demon Hunter lore brought in. Azeroth is a weird place with lots of weird people where weird stuff happens so after a while you just start going along with it.