Hi James,
Sounds like an interesting project... I would really like to hear how it goes. With a cellular connection, it could allow for some nice remote projects.
Maybe something like http://www.adafruit.com/products/390 for the solar charging... It's for LiPo and only 1S, so you will need a step-up system in addition. I haven't tried it, but the stuff from Adafruit is usually pretty good.
As I remember, most SBEC can be used with NiMH, but you will need 6+ cells to get a high enough voltage on the input side.
/Thomas