mstdn.starnix.network is one of the many independent Mastodon servers you can use to participate in the fediverse.
Starnix is a Fediverse/ActivityPub Focused platform. Topics are mainly Technology and computer related but are not required to fall into those categories.
Maybe??? But last time I checked Misskey is not Mastodon API compatible, so you'd need to find a client that can interface with its specific API. You can't use Tusky/Husky Bloat Soapbox last time I checked.