Is my plan for a shed base on pre-cast concrete supports reasonable?
What's the purpose of the two blocks in the center? Unless they're support a beam, they only effectively support the individual joists they're under. I would't use them. Worst case scenario they cause bulges in your floor.

The metal angles are also unnecessary. The fasteners you use to connect the joists (galvanized 20d nails or 3" coated screws), along with the floor sheathing, are adequate. 

Finally, ask yourself whether you actually need the pyramids. Your PT lumber is rated for ground contact, and raising a shed that high makes for access challenges. You'd probably need to build a ramp at least 4 feet long. I've built two such sheds at my homes and simply rested the 2x4 floor framing on a washed rock base. If you do that, lay housewrap or poly sheeting under the floor sheathing to protect it from excess moisture. 

I don't know what "cross members" are, but blocking isn't really necessary for an 8' span, in my experienced opinion. 

Otherwise, I think you have a good plan.