Sue, I think you got great advice on your previous post. (I wish I got the class of response you got)
It looks like you have the determination, you only need to build up the mileage. Just be careful, 10% per week is a lot, but maybe with your xtraining experience, doable.
The key is distanced and endurance. I've been doing 45+ miles per week and feel I can only do a 21k in about 1:50-2:00 range. I need to work more distance more time and the, maybe then, work on speed to really race a race.
Fit in 10k & 21k races in your schedule as part of the training for the marathon.
Those are my thoughts...