As a future investment, you might want to take a look at this three charger unit from Milwaukee (which I'm sure you're familiar with already).. http://www.toolup.com/Milwaukee/48-59-0280.html
I'm planning on getting two of these to start, with an additional one later in the year.
As for your 10 pack, I knew you were going to put one together, I just didn't realize you already had! Awesome!
The fact that you're incorporating older batteries is a testament to your garage engineering sensibilities (i.e. always on a budget)
What type of controller are you working with for this setup?
I tried finding the information on your profile, but there was nothing listed.