I would just stick to Selaginella species in containers of your size. The soil could be 6 parts by volume of fresh water sand and 4 parts by volume of milled peat moss. Blend well. Probably no more than 3 inches deep. Moisten it well and then squeeze it out before putting into your terrariums.
There are several species of Selaginella that are easily purchased that will suit you. These should be kept in a cool room with bright light but shaded from direct sun or outside on the porch in shade. They can easily handle temps down into the 40Fs.
I can only recommend this one retailer as they have the best selection AND THE EXPERIENCE of growing them. They are in NC and will take visitors by APPOINTMENT ONLY. Check website for info. Better to visit and save on shipping charges!! The link is
http://www.plantdelights.com/Selaginella/products/344/
to see the Selaginellas. They look nice! and are not available elsewhere except for a few they list.