Need help with my marathon schedule

Pipski

I am a first time marathon runner.   I'm an average runner...I run at 9:20 minute miles.  Would love to get faster though.   I have ran half a marathon, but was running at 10 minute miles back in 2011.  I run about 15 miles a week and weight train on my days off.  So this is my predicament.   I am following the Hal Higdon training programme....Novice 2.  I have been advised to start using the programme now and then revert back to the beginning, to prevent injuries and to help me build up.  My predicament is this.  By the time I get to the start of my 18 week programme (mid December), I will be running half a marathon.  I would have already completed 15 miles and then the week after I run half a marathon.  When I re-start Hal Higdon's training scedule, do I go right back to week one, where I start at 8 miles on a weekend?  It seems quite a fair amount to jump back?    However, I am aware that I don't want to over do it, with all my training!   Also, on my days off I weight train.  I will still continue to weight train twice a week.  I will probably only have one day of rest.  Is this ok?  I would hate to loose my definition in my arms, as I do enjoy my body building.  Thanks guys,