The resources required by federating depend on how many people follow each other across those two instances and how much these post. Just existing and theoretically federating doesn’t need any resources if there’s nobody following, assuming threads isn’t doing that different from everyone else.

For each post a user makes on your instance, it sends that post to each instance where someone follows the poster. There’s no automatic sending to every known instance of every post on your instance.

Every image on the federated timeline. It’s a lot if users on your instance follow many other users.

Unfortunately not. I think some areas have hashtags for that kind of stuff and someone is working on a new platform, but it’s not there yet.

https://codeberg.org/grindhold/flohmarkt

It think it’s a fire and forget kind of app, so I wouldn’t expect any updates besides occasional dependency updates.

The F-Droid app is basically a browser that lets you stay logged in which is quite comfy.

Joining the channel and ask would be the most straightforward way I think. I kind of misunderstood your initial post. I know there are several different “Fedimins” communities, but I only participate in one that’s specific for German instances (of all kinds).

There’s also https://socialhub.activitypub.rocks/ Idk if they have a matrix room/space