Yes. You can easily spot them, either with masto in the name of the user instance or from the fact that the post or comment will contained mention in the @user(orcommunity@instance format.

Yep all the time. Other platforms allow you to subscribe as well.

Piefed you can subscribe to individuals like they are communities. Works really well.

@Wanpieserino
Only if those posts are to/mentioning a community on Lemmy or Mbin. Profile/public posts don't show up on Lemmy since Lemmy requires all post or comment content to be associated with a group actor (AKA the community/magazine).

@mesamunefire
@fediverse