question 1: is there an index of all platforms/servers implementing ActivityPub and/or OStatus which are all connected in a mesh?
or a list of all meshes and then each mesh with the list of all servers?
question 2: who’s running each server? and who pays for the resources needed to run a server? and if that server gets corrupted and my account is stored there, is my account compromised and in danger to lose all the data, all the account? or it gets duplicated on several connected servers which are in the same mesh?
ActivityPub (and OStatus before it) doesn’t have the concept of a server being “connected” to another server. Instead, users follow other users, and messages are sent from your server to all of your follower’s servers. We call this a follower-based network, and it’s very much an evolution of feed-based technology, like RSS readers with real-time notifications.
I don’t think anyone has succeeded in mapping this out completely, although there are some graph-based visualizations out there. The most up-to-date list of all ActivityPub enabled servers (that I know of) is https://fediverse.network/
Servers can be run by many different people. For example, I could run a server just for my friends, or a server for model airplane enthusiasts, or a server only for people from Portland (this one actually exists). Costs can be paid by the admin or split by the users using a crowdfunding system like Patreon or OpenCollective (many instances use Patreon).
Currently, if a server goes down, you lose your account, but we’re looking for ways to improve that. And of course Mastodon supports data export, so you can export a copy of your data at any time. You can also migrate servers by sending your followers a “Move” notification that automatically subscribes them to your new account, but right now that requires the original server you’re moving from to still be up.