A specific instance (like BeeHaw) can defederate other instances. It's basically like blocking that instance so users on BeeHaw can't interact with that instance.
2 as of today. My main is on BeeHaw, but I realized that some of the communities I wanted to follow were on defederated instances, so I signed up for programming.dev. I think I'm going to use it for the tech-related communities (plus anything defederated) and BeeHaw for the rest
How do you approach testing your backups? It seems like you shouldn't just restore it to the various applications because if it fails then you're screwed. But it also seems like a huge pain to create duplicate instances of every application to test the backup.
I like Firefly III (https://www.firefly-iii.org/) as a self hosted option. There are various importer tools, although the developer's general feeling is that you should do it manually. I personally imported a few months of transactions to seed it but have been doing it manually since.