How high should I make my yurt platform?
Other things that come to mind that you may want to check out before deciding on the height:


What are your local zoning laws?  You do not want to make something too high that violates some local code (although from your description of the platform this may not be an issue).
What type of clearance do you need (if any) above and around the platform?  Any low tree branches or wires you need to watch out for?
Make sure to take into account how it will appear from the street or back of your house or however someone would look at it.  What is the grade as someone approaches the structure?


Other than that you covered a good number of the items to consider when determining the height.  The deciding factor here appears to be how the final structure will look in your yard... and probably you want to minimize its size/appearance as much as possible.  See if you can position it just high enough to get air flow under the structure for ventilation (to keep it dry underneath) but no higher.