Interesting idea! I have some thoughts if you’re open to feedback:
Always!
Have you considered moderation? These mirrored communities on lemmit.online will still be getting comments from all over the federated network, and if you’re the only user and sole moderator of every community, then it might get quite overwhelming!
I have, and I hope it won't be a problem ;) I'm a software engineer, as mentioned above, have little interest in managing people outside of work :P If anyone wants to become a moderator, they're free to request it.
A small VPS might not be able to handle that
We'll see how well it does. I don't mind spending a little money on this (few dozen €/$ per month), if it takes off. In the end though, it's more meant as a kickstart for Lemmy content than anything else.
How are you planning to deal with API limits from Reddit?
HA! By not using the API. For starters, because someone-who-isnt-me would like to browse NSFW content. I do a bit of client-side throttling between requests, which I hope will keep me under the radar. But it's mostly based on rss for the subreddit overview, and scraping for the individual posts.
In the end... we'll just have to see how it goes.