There is an awful lot of ground to cover here.
As a distance runner (4 marathons) and Physical Therapist, we could chat for hours. It's like asking "what do nurses do?"
Best advice that I can give 'off the cuff', is to pass on what was given to me.
1) Good shoes are essential. No one brand is superior to another; you have to go with what feels best on your feet, then some trial and error for what gives you the best support. Some people swear by Nikes, others by Asics, others New Balance, Saucony, etc. Personally, I find that Asics are the most comfortable ride (gel is good stuff!), but don't last very long. New Balance don't cushion quite as much, but the shoes last much much longer. The gel in Asics just seems to break down after about 2 months of serious training, where I can run in new balance upwards of 4 months if you keep 2 pair and rotate them daily.
2) Don't increase mileage too much, too fast. You can avoid a host of orthopedic injuries and muscle strains by *slowly* increasing mileage. Even though you feel just fine, etc.; the body will adapt to stresses increased over time, but will lead to injury if you increase too much too quickly. We're talking about 1% per week increases - no more.
3) 26.2 miles is a long long long way :-)
Actually, it's a lot of fun when you get into it - but proper training will take a heck of a bite out of your time for anything else. This is true for marathon training, at least.
I haven't had the time to devote to training in about 4 years; hence no marathons recently! You can still enjoy running w/o becoming an addict, but if you do get 'hooked', you need something like eight hours per week to properly train to run the distance without injury.
Hope this helps - and best of luck!!!!!