Yes, it’s a small instance I’m only intending to use it myself, maybe some other friends later.
I’m doing it in a VPS with 1 core, 1GB RAM and 25GB SSD (it’s the smallest one).

The only problem I had was because the documentation is a bit outdated, after fixing a single configuration everything has been smooth, I can easily subscribe to any community from any other instance and I can interact no problem.

I think each instance has a copy of the posts and comments.
For example this post in my instance is https://lemmy.pe1uca.dev/post/834
But the original one is https://lemmy.one/post/22814
And then in the instance the community is hosted is https://lemmy.ml/post/1159362

You can see the ids are different, so if lemmy.one goes down each instance already has a copy (except the images).
What will probably fail are the interactions, the original instance won’t have the new comments and votes. I’m not sure how it works after it comes back online.

AFAIK, yes, the answer to have control on which instances are blocked is to run your own instance, that’s actually what I did.

For a way to search the number of instances that block certain instance, I don’t think there’s something like that yet.

Let me clean my backlog of unfinished projects (now less with reddit API soon to be dead), learn rust and kotlin to start helping :)