Well, I can fully understand how cold can interfere with running... I have the same issues at the moment. Regarding the marathon plan: it looks like fine, ordinary, not a too strenuous training plan. Since you intend to use it as pre-plan prior to your final plan and this one is meant more for building the "friendship" with longer distances is a very nice one. It also has weeks with "shorter" long runs (like "resting" weeks). Maybe you would like to add also speed work to help you improve the pace and make the training less dull, but you can easily do this with transforming one of the medium lengths runs into speed work. Onward and upwards!
The goal will be to finish it, my motivation is to do one marathon before I'm 40, which is next year. So speed is secondary to building up the stamina and avoiding injuries. I'm also afraid if I went for speed, I'd need more help to tell me how and what to focus on, which I don't really have the time for, does that make any sense?
You are right: focus on stamina and avoiding injuries is much more important. Perfect approach. This plan will bring these results. Fingers crossed and onwards and upwards!
Thanks for your support!