Back with newsgroups the general rule was to go from general to specific. You start with a general discussion group and when discussions about video games get annoying you create a games group. If then there are too many Baldur’s Gate discussions you create BG. If they are dominated by Baldur’s Gate 3 you create a Baldur’s Gate 3 group. If everyone is fawning over Withers you create a Withers group which of course will be flooded with discussion about the Withers’ tits mod, which shall get its own group.
Meaning you should create a group when demand is there and not the other way around.
It’s definitely fine if you’re okay to be the sole poster on that community.
Based on the weekly fedigrow posts, it seems like the majority of people still prefer when they are other posters, as it kind of relieves them of the weight to keep the community active on their own.