A strange coincidence there, my first marathon was the FLM 2005 when I ran for the RNIB too. It was a blooming hot day but a great experience. I'm sure you'll love every minute of it.
I got my first schedule from Bob Glovers " The competetive runners handbook " and started with a base mileage of 20 miles a week for one month before starting the schedule, which peaked at 40 miles a week with 8 weeks to go.
The schedule was for 16 weeks and suited my plan of just completing the marathon without putting pressure on myself with a time.