To the best of my knowledge; all bar adaptive are streamed via RB. Could = already in your RB account. Torrent= scraped from a torrent site, then downloaded to RD (or most of the time already in RD cache). You stream from RD. Hoster: direct from a web hoster and streamed via RD (personally I find these of little use). Adaptive= I believe this is only if you have legit services linked (e.g. netflix). I don't believe it's been implemented yet although I may have missed it. Hope this helps.

Ask far as I know (I'm a user not a dev), it shouldn't make a difference as all come via RD, so the speed or buffering will be dependent on your internet connection and connection to RD servers.

I personally turn off hosters and scarpe only one torrent site (torrentio) as it's super fast and gets enough links). But I use fen primarily, with Seren as a back up.

I have fairly slow internet and never have any buffering issues. I would suggest looking into your video cache setting (Google Kodi advanced XML settings link to Kodi guide) or set Seren to select only smaller file sizes.

Me too! I've joined the discord server, but it's not really the same. I know the sub-reddit is still there but I'm loathed to use Reddit at all these days. What I found best about the sub-reddit was the troubleshooting and heads up for issues. So many times I would have a issue, check in on a4k and solve it right away. Now I bounce between the github pages and discord. But to be fair it's been a trouble free experience of late.