First by picking plants that are suitable for growth in a terrarium.....which pretty much precludes any cacti or succulents, as they 1) require very good and very fast drainage, both of which are not available in a terrarium and 2) avoiding any atmpsphere that tends to increase humidity and reduce air circulation, which these xeric plant detest.

GG, since my experience with xeric terrariums is different from yours, I feel the need to comment.

Since the culture of plants in a terrarium cannot be compared to any other container growing, the need for excellent drainage is a non issue, as far as I'm concerned. One shouldn't water a terrarium enough at any time for excess water to ever be a problem, no matter what category of plants.

I used to grow (and sell) terrariums with cacti and/or succulents with great success. I chose containers with an opening rather than one that creates a tightly enclosed environment. A terrarium container doesn't have to be without an opening for it to qualify.

The article in this post, though, raises more questions than it answers. For example, in a sealed terrarium, one needs to be very careful about the amount of window light. Plants can be cooked in a moist, sunlit, air tight glass container.