This is a ten minute routine that you can do daily if you wish, not just before running. Later you might want to try some of the other routines and clips shown on the right hand side of the screen.
A visit to a physiotherapist might be useful from the point of view that if there is something you should not try to do you may as well know about it now. Also some massage may help loosen up anything that needs loosening.
You have been managing injury and it is your first marathon. Two things there a) you do not want to make your injury any worse b) you want to start your marathon and get round.
Two basic purposes of your 20 mile runs is 1) time on your feet and the associated psychology (confidence-still 6 more miles to go) 2) your body learning to utilise energy reserves efficiently.
Your own plan would be fine without the injury but you need to be realistic. I think Hal is leaving you too much to do on the day ( but humbly admit I may be wrong!). His solitary 20 mile is 5 weeks out from the race! I think that will count for nothing on race day. If you feel you are managing injury well I would suggest
12 miles 16 miles 14miles 20 miles 12 miles 20 miles 8 miles Race day
Remember these runs should be slow. You can wear long compression socks and leave your watch at home. Each week the longer mile run is followed by shorter. You get 20 miles 4 weeks before the race and 20 miles 2 weeks before the race. This will boost confidence on the day and may just help your body to use fat reserves.
If you injury is not coping I would suggest keeping your solitary 20 miler to 2 weeks before the race ( essential that your body will remember what it feels like) and then just do what you can mileage wise for the next 14 days with rest being paramount.
I have just bought two pairs of Lunarglide 5 after being pleasantly surprised by the version 4. Cosmetically there are some differences. I have run twice with them and they seem fine.
Since you are asking a very basic question it is likely you are new to running. Either your feet are too broad for Nike or as Nick Windsor 4 says "have you got the correct size?" I believe a rule of thumb is you should be able to put two fingers down behind your foot while it is in the shoe. Your foot will expand while you are running and needs room to spread but surely Sweatshop would take that into account? If you are new to running then your feet may still be too tender and may need some time to adapt to the force of impact.
Sounds like 'shin splints' (medial tibial stress). In addition to managing the condition you need to ask what has caused it.
Too many miles on a hard surface. Not increasing your mileage gradually some say only 10% a week. Not giving your legs time to recover. Running can cause microscopic 'tears' and contusion to the soft tissue in your legs. This is caused because your tendons and muscles have not developed sufficient elasticity to cope with the workload. You need to let the natural healing process take place which cannot happen if you keep teasing the damage.