Autofocus points will be an issue, you can get around those in Nikon (all AFS lens have manual override so you can focus wherever you want ) don't know if you can with canon lens? Someone please pitch in on that.
The worst mistake you can make is thinking you'll be set with one lens. The only reason I suggested the 6d was because of budget, I would personally have a body with almost the same performance as the mk3 and buy more glass. If money wasn't an issue I'd say mk3 without a doubt
If you can rent lens or borrow perhaps, buy the body only and buy lens later based on your experience, camera bodies come and go, lens dont.
Well as I said, I can borrow lenses from the school for free next semester. So with that said, the MKIII and 24-105mm should be fine for everyday shooting right? or is there a better lens I can get? Also do you guys know in the future, if I am going to pick up the Sigma 18-35mm F1.8 if that will work with the MKiii?