There's tons of info on MS out there. Here's Wes Dooley's AES paper that goes into lots of detail:
http://www.ribbonmics.com/pdf/technique.pdf
But a google search will turn up all kinds of info, tips, etc:
https://www.google.com/search?q=mid-side
Here's a couple of the first hits:
http://www.soundonsound.com/sos/mar1...-tech-0311.htm
http://www.uaudio.com/blog/mid-side-mic-recording/
I think MS is perfect for what you want. If you want to create an artificial sound stage by paning mono sources, just use an MS decoder and spin the dial to get mono, then pan. If you later decide the guitar should be in stereo, add back in the sides.
For a "big" guitar sound in the mix, I'd consider leaving the guitar in stereo. But of course, I haven't heard your mix, so it's hard to know for sure.