I already created the discord server a long while back when I was at r/RedditAlternatives, people knew what it was and many average users were already on the platform hence accessible, matrix is great but still not at a stage where the average person uses/knows it compared to tech nerds or enthusiasts, besides we already have around 100 people if not more on the discord server, reusing it made more sense for now although I wouldn’t mind creating a matrix in the future once the community grows to offer another way of keeping in touch with our community for those who have or are ready to go to Matrix :)

https://github.com/jwr1/interstellar

I think a good starting point would be advertising Lemmy where possible on your subreddit, such as pinning an equivalent futurology community from Lemmy linked to a reddit post and pinning that, also mention your lemmy community on other places like mentioning Lemmy and asking users to consider Lemmy instead on the welcome message when new users join/subscribe to r/futurology.

Kbin has this figured out, they now have an in-built community request system.