I think the amount will depend on you. Are there any hobbies you have put down and come back to before? I'd start with those, and expand as necessary. I've also found it helps to have hobbies with different levels of energy requirements. Writing, for example, take a lot more mental energy than watching Star Trek, so Star Trek is a good fallback for me. Often watching an episode or two will be enough to get me in the mood to read, or write myself.

TTRPGs are high energy investment as well, but they have the added benefit of being a group activity, so there are other people I'm motivated to not disappoint by flaking. I would definitely recommend a regularly scheduled social hobby. It can be a lifeline when everything else is chaos