Cool pictures Flusher. I like the colours on your guy, looks very nice. Mine is the same green all the way to his tail.
In terms of what they'll eat, I think they'll eat most any edible food they can catch. Mine has been eating frozen mysis shrimp and some pellets for now. There is a much larger resident Hermit Crab in his tank which may someday become lunch...
The Smithii will get as large as 3". Some species will be smaller and there are some that will be larger.
Here is some great info and pictures:
http://www.ucmp.berkeley.edu/arthrop...html#directory