I'm currently in week 12 of a 16 week London Marathon training plan - managed 19 miles in 2hrs 40 mins last Sunday, got a 3 hour run this weekend to check off

I'd done a half marathon some years ago, never really minded road running, just decided that at some point in my life I had to do the London Marathon. Luckily I work for a charity, so got in on one of their five places...
I plan my run on google maps - usually do a big lap of surrounding villages, but you can set maps to walking routes and work out a pace from the distances it gives you. I've got a Garmin watch which you upload onto their website and it analyses data - great for data geeks like me! Really does help with your strategy though.
I've had trouble with blisters and achilles/calf issues. Been to a physio twice - its all about the stretching and after a run, take a couple of ibuprofen and use arnica cream (natural muscle remedy) on your calves. I can also recommend Skins compression recovery tights - not cheap but definitely worth it!
Re; footwear, the research I've done and spoken to frineds who are serious runners (Mararhon vets, Marathon Des Sables runners) have said that as many who buy off the shelf shoes as those who spend £100+ on shoes as a result of gait analysis, get blisters and issues with their feet. Find a pair that's comfortable, about half a size bigger than you usually take (feet swell when running) and make sure to vaseline your feet before you run anything over 5 miles. That should avoid any issues. Go for a structured pair of shoes - they are the best all round and unless you're planning on changing your running style to planting the ball of your foot as opposed to your heel, avoid the 'free' running shoes. I've had both and would go with the structured shoe.
I've learnt a lot about running technique, re-fuelling and post-run recovery - there's some great info out there but you have to find what works best for you