What do you plan on growing? From your question, I gather this will be a planted terrarium. I set mine up: Substrat of granite stone 3 cm high. This also houses piping for drip the system. A nylon mesh (for windows) to prevent soil going down. 10-15 cm of CP mix. At the moment I have Ultricularia in the bottom, and hanging a nep. Water table is kept around 10 cm, and I check periodicly the TDS. I grow also other things in there, and there are areas with more lighting, and areas with less.
It depends on what you want to grow. You can have areas with higher water tables by placing a plastic container buried in the soil. Drill holes in the side of the container, at the height you want your water level, and bury a drip hose connected to your watering system. This way you can have an area with a higher water table, and any excess water flows out and in to the general terrarium. I set this up for Utricularia in my terrarium, with a higher water table then the rest.
I have 3 flytraps. Gremlin, Dente and Red Piranha. Drosera capensis 2 varieties, D spatulata, D x beleziana " Nightmare". D intermedia x cappilaris, D dielsiana, S. flava, s purpurea venosa, Nepenthes ventricosa, Pinguicula x wesser and Utricularia sandersonii. The temperate plants will be sunk into the substrate in their pots so that I can remove them to my refrigerator for dormancy. The others will be unpotted and planted, except for the Nepenthes, which will be left in its pot on a flat rock. I could probably dig a small depression in the substrate for plants like Utricularia that need to be closer to the water and build it up for those that like it drier. I don't know which those are, but I'll find out.