I don't believe there's a limit. My instance certainly doesn't have one. If there's a void and you feel like you'll have a reasonable amount of content to share over time then why not? I've probably made close to ten. Everyone's always saying we need more niche content, right?

Only potential pushback would be that too much of the fediverse is consolidated on lemmy.world as it is and new communities may benefit by being spread out on other instances.

But overall more is always better regardless.

Edit: try to spread things over days/weeks too to ensure a steady stream of content. If you build it [they] will come.