Try going to the home page of instances of accounts you like (or of instances that seem interesting) and browsing their federated feed (tap globe for “live feed” then hit “all”), you can discover tons that way.
As a general mastodon instance mas.to looks good and is a nice size with a good stable history.
You can find established, more established instances on the fediverse by surfing around a bit fedidb
A bridge is a tool for connecting things don’t connect, it is not federation.
The relay layer/app view forces you under the control of a centralized system at a fundamental level with bluesky, the only thing meaningful about that kind of federation is hosting costs for processing and storing post data are offloaded onto the user.
…Which when you think about it is actually pretty fucking insulting to the fediverse and what is trying to be when bluesky pretends it is aiming for true federation and decentralization.