If a community appears as a 404 page when you click it, it likely means that the community is being hosted outside of the instance you are currently using and that nobody in your instance has viewed or interacted with that specific community yet. In order to address this, you will need to copy-paste the specific handle for the community (for example, [email protected]) into your searchbar so that your instance can "learn" that it exists, after which the community should display via linked URLs without issue. Hopefully this is addressed by the lemmy devs and streamlined in the near future.
In order for a community to show across instances, someone has to search for the full community URL. I have a separate account on Lemmy.ml so I went ahead and did it.
Fair enough. I think it would make you a mod by default. Not that there's too much to do when the community is small, but if you are busy I get not wanting to add commitments.