I put gravel in the bottoms so water could drain away from the roots and then added a layer of sifted compost on top of the gravel.
The moss, lichen, fern, sedum and hen and chick (should that be hen OR chick since there's only one??) are all things I took from around my yard.
It's been my experience that moss grows where it wants to grow so time will tell if it will thrive here. I have been putting tops on the terrariums at night to raise the humidity.
These giant snifters didn't come with tops so I use a glass saucer on top of the largest one and I found two small headlight lenses (no kidding!) at the VofA and they fit nicely on the smaller ones. They look kind of cool, too, in a funky headlight kind of way. If everything thrives it won't take long to outgrow these little homes but I'll cross that bridge when I get to it. I've only got $6 in the whole she-bang and I'm loving them all for the right now.
I have them sitting on this little table next to the hot tub on the patio. I made the mosaic table several years ago. If you look at the first picture you can see the pottery shard mosaic on the top and the bottom edge is decorated with key "fringe". The granddaughter loves to run her hand across the keys and make them jingle. It's a happy sound.