He's going the distance, he's not going for speed

I am looking for a little guidance to help me connect the dots to 2.4/112/26.2 in 2008.  I started this quest a little over a year ago and after biting off more than I could chew in the training department, I've settled into steady progression that has me pretty psyched.  I started out with the HIM plan but with no run experience, I got sidelined after a month with ITBS.  Sorted that out and made it through the Oly plan.  Raced it in the gym (=Kestrel Talon in road position on a trainer and treadmill) as a duathlon since I was stuck on the ship I work on.  That was Labor Day.  I took two weeks off and started the HIM plan.  I was again stuck on the ship in Feb when the plan was up so I raced it again as a duathlon (the Talon in aero this time around).  I lost 3-4 weeks of training with pneumonia and tried for waaaay too many calories in the race simulation so it didn't go well but I finished it and learned a lot.

After another 2 week transition, I've jumped back into the HIM plan in hopes of making my first real race - the Honu HIM in June.  I'm aiming to do the Honolulu Marathon in December and then shoot for CdA or Chesapeake Man in 2008.  My question is this...(#1) does it make sense after training pretty consistently for the last year to take a month or two easy, then just do the 20wk mary plan or would I be better served following the IM plan once through to the marathon since my goal is volume and not time oriented?  I'd hate to lose fitness and all the hard work by slacking off but don't want to self destruct either.  Other than illness, I've been healthy and only feeling challenged, not over trained.

I am digging the running now and finally cracked a 10' mile pace for a training half mary a few weeks ago.  Still, I feel the marathon is a psychological barrier that I have to get over before toeing an IMTBD line.  I'd like to improve on my 18mph average on the bike but am comfortable on the bike and have done some centuries in years past.  The swim will be what it will be, I can't do anything more than swim cords on the ship (water, water everywhere and not a drop...) but I've found it takes about a month to get my arms and swimming zen back so am going to try and maneuver work sked to give me 2-3 months of vacation before IMTBD.

Oh on a sidenote...I'm 5'6" and 164lbs at about 11% BF.  The Talon has 172.5mm cranks and as I tip further into aero, it seems to get harder to maintain 90 cad.  From what I've read and measured, I'm on the cusp of between 170 and 172.5.  I jumped on a P2C at the LBS the other day and it felt like "home."  I'm still not sure if its the extra 3 degrees, the VisionTech cockpit, the 170mm cranks or the lack of a compact cluster.  Maybe its all that, maybe its just the Emperor's New Clothes and bike envy  I loved the Talon with a road cockpit but am not so thrilled with it in aero.  I'm going through a serious tweaking stage, pasting pics into CAD and drawing angles, trying to make sense of Empfield's manifesto on aero fit.  I need to stop the tweaking in the next week or so in order to settle in to a position in time for Honu...(#2) is it worth shelling out the duckets for a 170mm crankset???

Thanks BT'ers - you're great.  Video may have killed the radio star but BT saved the newby triathlete 8^)