None or about a dozen, depending on how you want to look at it.

I have about a dozen accounts on various instances, and four or five that I use regularly, but they're not really "alts" since they're all the same name - Rottcodd. Unless someone checked the @s and compared them, they likely wouldn't even realize they're not all the same account.

I started out doing it that way because when I first moved here, I just signed up for whatever instances looked appealing for whatever reason, just to try them out, and figured I'd settle on one later. I kept doing it that way because I discovered some advantages.

Each instance actually feels a bit different, since they have different moderation policies, different sets of federated vs. defederated instances, and different sets of communities that members have subscribed to, so different Alls. And I've emphasized that by having different subscribed and blocked lists on different instances.

So if I want to wade through chaos and maybe do some shitposting, I have an account for that. If I want to read or post about gaming or technology or popular media, I have an account for that. If I want to read or post about the arts, literature, society, philosophy and the like, I have an account for that. And if I just want to see comfy, pleasant stuff like cat pictures and recipes, I have an account for that.