I would lay out your plumbing first. In fact, if possible, you may want to consider radiant floor
in the slab (depending on your location and budget). Radiant
is IMO, bar-none the best form of heat for a yurt. It is efficient and it saves you precious floor space.
I myself would
not go with the square. It would make it hard to anchor the yurt for one thing. If you make a round one, with a wooden edge, you can anchor the lattice to the edge. That is pretty important. Otherwise, you will have to embed anchors into the slab and anchor the second platform to it. Yes, you will need to build a platform on top of the square slab because the yurt wall should overlap below the floor so rain water flows past the platform to prevent flooding.
Depending on location would also dictate a round single platform being a better idea. Imagine if you will, snow melting on the square platform and the water rising up above the round platform on top of it. That could get wet fast.
Please do let us know how your permitting process turns out. We get A LOT of questions about that here, so any information you can throw our way will almost definitely help someone else in the future.
Thanks and good luck!