"Off" season

Well, I've spent the last few weeks chilling out and not trying too hard to do much of anything.   I've taken the mountain bike out most weekends and had some fun discovering a new aspect of this crazy sport I've decided to make my own.    In the back of my mind, however, I've been ruminating on my plans for the off-season.   I have high hopes for next season, from doing my first (and subsequent) tri, to doing some serious riding -- and all of that will require that I am in better shape than I am right now.  

Next week marks the start of my off-season training plan.   It's a bit ambitious, and I'm sure it will be tweaked along the way, but this is what it looks like so far.

Monday - Morning swim (technique), evening spin
Tuesday - Morning strength (legs/core), evening run
Wednesday - Morning swim(endurance), evening run
Thursday - Morning strength (arms/core), evening spin
Friday - Morning swim (easy swim) -- Rest day
Saturday - Morning spin, afternoon run
Sunday - Strength (core focus)

I've never tried to put together a strength routine before.   My focus is largely on my core, as I need to set that right to avoid the mid season back issues I have had the last two years.   However, I want to work on arm and leg strength as well, for power purposes.   The following is my rough plan.

Legs:
10x Squat
10x Reverse Lunge
10x Side Leg Raise 
10x Calf Raise
10x 3-way Lunge

Core:
10x Windmill
10x Knee Cross Crunch
10x Prone Snow Angels
10x Plank w/ Knee Bend
10x Exercise Ball Arch

Arms:
10x Standing Shoulder Press
10x Prone Press
Push-ups (to exhaustion)
10x Skull Crushers
10x Chair Dips

Feel free to offer suggestions if you are so inclined.  I'm very new to this.