Thousands of runners complete the London marathon each year on a lot less that that - some of them in decent times.
OK, a 4 day week will never see you get to your ultimate potential, but this is your first marathon. Anyway, my experience of following marathon training schedules, usually including only 1 rest day a week, is that often they leave far too little time to recover from the exertions, and I risk ending up exhausted, de-motivated, or ill or injured. The body needs time to recover and build strength. This is the major threat to novice marathon runners, so many are forced to drop out because they over do the training, build up mileage too quickly, or don't build in enough rest days. The intense training schedules are aimed at experienced runners who are more likely to have the sense to back off when they are over-doing it.
I have in the past usually tried to trim the suggested schedules down to the core days, as advocated in last month's RW, and so run only 4 or 5 days rather than 6 per week. I have found this works much better - it has delivered times which while nothing special have left me very pleased, as I consider them to be a fair reflection of my (limited) abilities.
Maybe I am a wimp who needs more rest than most. But, the 4-session schedule sounds sensible as despite neing a novice you clearly are starting from a reasonable base of running fitness (the mix of tempo and speed sessions would be a strain for someone without an established base). The usual rules everyone says apply - build up the long runs and overall mileage very gradually, have an occasional easy week, mix in some variety (different surfaces, hill work, different routes and times etc) and make sure you get some race experience - there are several good half marathons towards end of Jan/start of Feb?
Best of luck.