The cave is to reduce the need for cosmic ray and micrometeoroid shelter (it's easier to build in a balloon in a cave than it is to build on the surface and fortify it).

Moon dust is toxic and jagged ( https://www.esa.int/Science_Exploration/Human_and_Robotic_Ex... and https://www.livescience.com/62590-moon-dust-bad-lungs-brain.... ).

> In several lab tests, a single scoop of replica moon dust proved toxic enough to kill up to 90 percent of the lung and brain cells exposed to it.