It depends on the type of content you’re wanting to do.
If you want to do more casual things on them, then swapping would be pretty simple. Both specializations share the same stat priority, so overall you’d be fine.
If you want to do Raiding or Mythic+ I’d recommend having DPS and Tank specific trinkets, as that’s where the gear really differs. Same thing with your Cyrce’s Circlet gems.
As for difficulty, I feel like Vengeance is in a good spot to learn. A couple things to remember is using your defensive before you pull and utilizing soul generators/spenders so you can keep yourself alive. Both the Demon Hunter Hero specs are pretty passive so you won’t have to worry too much about being active. I recommend Aldrachi personally since it really builds into the idea of making/spending soul fragments.