What is Reddit's opinion of XBian?

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This. Buy a Raspberry Pi, install Xbian. And voila you have a nice interface, couchpotato, Sick Beard and a torrent client running 24/7. And the best part is that it consumes nearly nothing.

This is probably one of the coolest things I have. I installed XBian on it which is just a modified version of XBMC where I can stream video from local/network storage. It plays 1080p video wonderfully and you can even get apps to play Youtube or Rooster Teeth videos.

Sorry, this isn't directly related to both of your questions, but regarding question #1, are those the only ones you have considered? Xbian I found to be the most feature rich and lightweight: http://www.xbian.org/

How have you installed Kodi (XBMC)? Easiest way would be to install a distribution with media center in mind - XBian and OpenElec both have versions especially for Raspberry Pi, so out of box I imagine those would be easier to set up to avoid any kind of potential compatibility issues.

Instead of raspbian you could give xbian a look. It is debian apt based and XBMC (kodi) works quite well, very lag free experience.

I'm a moderator on the Xbian forums and we are always happy to help a new user get the most out of their raspberry pi.

http://www.xbian.org/what-is-xbian/

I haven't done a tutorial myself, lack of time and a spare Pi to test stuff. But you'll find plenty on the interwebs. I recommend you start by installing XBian (http://www.xbian.org) and then install the additional applications like Transmission through the provided xbian-config (http://wiki.xbian.org/Applications).

I would skip the Sickbeard version provided there and install bricky's fork from his github repo (instructions https://github.com/bricky/Sick-Beard/wiki/Installation-on-Unix). To do this you should be comfortable on the command line of course.