Wow Chris it sounds like you're learning fast with this new system! Good work getting it to talk to the computer!
As for getting a power tank, I would recomend steering clear of any product which uses normal SLA (sealed lead acid) batteries. "Normal" SLA batteries are not designed to be deep cycled ie discarged and recharged. I went to a battery specialist and bought a 20AH deep cycle gel battery designed for an electric wheel chair. I think it was about $150 but boy is is good! It doesn't need to be a gel battery, just ensure its good for deep cycle. Otherwise you can kill a battery quite quick if its not designed for the purpose. I'd also recommend one of the battery fighter type of chargers specifically designed for SLA batteries.
There are some good threads on this site about batteries if you search around.
So where are these photos you've promised??? We want to see it!