I would recommend the Pangea forums for the most crested gecko specific resources.
The Sri Lanka ExoTerra would be fine for a single male or two females. If you get hatchlings you will need to house them in something smaller for a while though, because they don't do well in larger enclosures when they are small.
84 degrees is too hot. You want to keep it below 80 degrees at all times for cresteds. Anything higher can cause stress, organ failure and death. Ideal temperatures are 75-78 degrees.