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I'd say to you to only run 5 days per week, rest is extremely important. By running 6 miles per day, every day, you're not improving - mix up the distances, routes and pace. Your weekly training programme should include one long run over hills, one speed session, one fartlek sesion and a couple of steady runs. Vary the mileage from 4 miles up to 22 miles (only do two 22 milers before the mara) and vary the pace from slow to faster than predicted race pace.
Protein shakes - most definitely, within twenty minutes of finishing your run so your muscles will repair more quickly. A good quality Whey will be perfect.
Try and include a couple of gym sessions per week too, if you can. Good luck with it!
Any more questions, just ask.