When the perceived problem is lack of content, why is the solution always to throw more bot posts at it? I’ve blocked or site-banned pretty much every bot account because they’re just adding dead end posts and noise.
For Mastadon content, Lemmy just needs the ability to follow individual users. Not sure if that’s on the roadmap, but it should be straightforward to implement. Same goes for other ActivityPub platforms. When user-follow is possible, that opens up many avenues for users to subscribe to just what they want.
What you’re proposing is not really adding content, just clutter and the appearance of content.
Give Lemmy time, and it will grow organically. Let’s not try to force feed it with reposts from bots. As people discover Lemmy, if half or more of what they see is dead end crap reposted via bots, then I personally feel that will be a turn off for many (which defeats what you’re trying to accomplish).