New Patio?

I've been wanting to get some stone work done in the landscaping. We've wanted a stone patio pretty much since the first day we moved in over eight years ago. We've landscaped lots of the yard, but this patio would be a really nice addition.

Below is a pretty accurate drawing of our current landscaping:



And this is what I would like to do. I would like to add a stone flagstone patio to give us an upper and lower deck. The problem is that the yard slopes quite a bit here, and there is probably a 30" elevation difference between the top and the bottom of what would be the patio. This makes it quite challenging for a do-it-yourselfer like me.



The blue represents the phase 1 portion; red is phase 2, and magenta is phase 3. I may do all three phases at once, it really just depends on cost.