We've already got a replacement that's owned and administered by users, with no ads, that can't be bought and ruined by billionaires: Mastodon. The ex-twitter employees are already running their own server: macaw.social
You MUST trust your administrators of the server, who in many cases just set the server up to 'help the community'. It's admirable of them to to it, but running any kind of server takes time, energy and effort for no pay. It can be a rough gig, see no further than 'mastodon.technology' for an example of what happens when 'life happens'.
Migration from one server to another is on a "Mother may I" basis, where you have to have permission from both ends to enact the transfer. If your 'I joined this Mastodon server because I couldn't find another' decides to shut down in a couple of months, good luck getting that history back.
The server relay feature is hap-dash at best, and both of the top two Mastodon servers don't even support the feature.
Those three issues are just scratching the top of the problems. At the end of the day, if Mastodon works for you, great. However don't lie to people by telling them that it is a full replacement for every Twitter user. It isn't.