Don't clone the track. Record it 2 different times in 2 tracks.....pan one right the other left. I tend to go 100% left and right respectively. Generally this is on the STRUMMED acoustic only. I try to get it as close to the same as I can knowing that there is ALWAYS going to be a difference and the result is a tight performance with a W I D E sound. All other instruments in the mix are closer to center and the mix sounds full as a result. The acoustics are generally mixed -12db or so... so they are not up in your face. They simply provide the ambiance needed. I do tend to scoop the mids out a bit depending on how it sounds to get it cleaner without the boxiness that acoustics like to produce.
Most all of my music uses this if there's an acoustic guitar in it such as here>>>>
http://soundclick.com/share.cfm?id=12024980 The mic you buy will depend mainly on your budget and what you can afford. I have a Rode NT-2A condenser that I use for just about everything and a dynamic SM-58 I use on cabinets. For the low budget, a company called Gauge Microphones USA has very inexpensive but good mics. (Mail order/internet only)
I would only use a built in pickup on stage to get the volume up and into the PA..... not so much in the studio. I have a guitar with a pizeo pickup in it and it works fine for stage and live performance where the sound quality isn't required to be perfect.