I am extremely short on time, so please forgive me for the short response.
First and foremost I commend you for putting this much time, effort, and thought into setting up the proper enclosure for a reptile.
Forgive me, but I feel this must be said. Please get the trial and error out of the way before introducing any livestock. Like most animals, reptiles hide there illnesses extremely well. For the novice keepers or even intermediate keepers it is not easy differentiating between normal behavior and signs of illness. Generally trial and error with reptiles doesn't end well.
The main thing is that the temperature should never go higher then the maximum recommended temperature for said species. Keep in mind reptiles can and will survive temperatures below what is recommended for them. They will not handle higher then recommended temperatures. They will actually succumb a whole hell of a lot faster to higher temperatures then lower temperatures.
As far as the visual aspect of the enclosure goes, I feel you are getting somewhere. You have to bare in mind deserts are barren places. Yes, E. macularius occupy kind of a oasis type nice in the desert but, it is a desert nonetheless. I would stick with a staple of grass like plants with maybe a broad leaf plant of two here and there for variety.
If you ever visit a true desert first hand you will be hard-pressed to find a area even twice the size of your enclosure with more then two plant species.
To reiterate my main point...
Get your parameters straight before introducing livestock.
Other then those suggestions you are on the right path. I feel your willingness to research and invest the time and money to make the perfect habitat for your animals needs to be noted, and I commend you for that. I see far to many people jump the gun when it comes to specialized animals care and screw it all up. If you ever have any questions for me my e-mail is firstname.lastname@example.org
. Keep up the great work.