Hmm so the Feed actor mainly consists of a following collection and uses Add/Remove activities. This really sounds like it should be a Collection and not an actor.

Ah its more complicated than I thought. We also have a similar or same feature on the roadmap, when I get to that it can federate with Piefed.

Neat, it federates. Seems to work similar to a normal community, so it should be easy to follow these feeds from Lemmy.

Its best if you improve the existing site, that way you dont have to worry about hosting, or directing users to your new site.