!lemmy_support@lemmy.ml seems overall pretty technical, but I've seen people post asking about how to use the site in general. There might be other communities as well.
Sync is my client of choice.
Really just Element, since every other desktop client lacks features and/or looks bad. The only downside is that it's an Electron app.
I'm not affiliated with Peertube development so this is just my understanding, but a video is hosted by the website just like any other platform, so a video without peers will stream you that copy and that's also why there is a storage limit.
Sharing a video over the WebTorrent protocol is mainly to speed up the streaming when say someone is closer to you than the server sharing that video.
Afaik, Peertube instances do allow you to copy a video's magnet link for you to seed with your torrent client if you're feeling generous. Anyone else feel free to correct me if anything is wrong.