I've been working on this rig, and here are a few screenshots of my progress. I'm still working on skinning the legs, and might go back in to the spine, as well.
Some of this has been pretty tricky, and I've had to fix a few mistakes, but I'm learning a lot from this. The legs have been a challenge, especially the back legs, because I wanted to add control for the extra joint, independent of the rest of the leg.
I have just done a basic skinning job on the legs, so far, I am going to work on improving this next. I wanted to figure out the rig first, so that I knew which joints I would have for skinning purposes, so I have been going into 'evaluate nodes' and hitting ignore all, to make it easier to paint the weights.
There's work left to do, but it's very satisfying to see it start moving.