If you use more than one mic, and record in a less than acoustically ideal room, I wouldn't go with the real stereo setups (spaced omnis, ORTF, X/Y, Jecklin disc, M/S...). Those are mainly for distant miking. That means you get a lot of room tone.
In those settings, the two (identical) mics are placed at the same distance from the source.
In my experience spaced omnis often sound more natural (or rather: wider and more relaxed) than X/Y, but you can get phase cancellation at lower frequencies when played back mono (which might or might not be a problem).
A nice setting is Blumlein (two fig-8), or the Jecklin disc. Both are less sensitive to room acoustics than spaced omnis.
BUT, as you are recording acoustic guitar in a home studio, try the "completely different mics in the same spot" and the "various mics in different near-field spots", and see what works. Always listen to the results of your mixing in mono.
You might also want to experiment with artificial room (not reverb, just some space / early reflections) instead of more mics. There are good convolution (IR) reverbs out there on the internet. Good reverb units are Quantec, EMT, Bricasti, Roland R-880, as well as the Lexicon units 480, 960, and 300. You can find free IRs of all those units.
Don't shy away from EQing the send or the return when working with reverb units (EQing before the reverb unit doesn't sound the same as EQing after it).
Experiment with placing of the room/reverb - a stereo reverb often sounds better when the two outputs are NOT panned hard right / hard left. Even weird settings can sound great, or reverbs that are completely mono.
Also, I would try to have a strong middle in the stereo field when mixing solo acoustic guitar. A lot of solo acoustic guitar recordings lack definition - there's sound everywhere, but no source (the guitar can't be located), and often it leans to one side or the other when played back over headphones (although the meters show the same level on both channels).
Of course, this depends on where you want to go. Some tracks sound best whit a wash of reverb and chorus...
As for phase cancellation caused by different arrival times (we call it Laufzeitunterschiede in German, I don't know the correct English term), a rough rule of thumb is that the mics should be 3 times as far from each other than from the source, and you're on the safe side.
You will always have phase cancellation to some degree if you use more than one mic in not the exact same spot. It's not just about proper distances, it's also about the radiation pattern of the instrument, early reflections, etc. You always have to check it anyway, by listening in mono and checking it with the Goniometer.
And again, experiment with bigger distances. Instruments tend to have a very uneven sound if you're too close (different frequencies are radiated in different directions).
And most of all, have fun, and enjoy the music. That's what it's all about, remember?
