Ground plants and misc. non-orchids for moist terrarium?

[Fishkeeper]

I'm gathering information and supplies to use in a terrarium I'm setting up. It's going to be a 12x12x18 Exo Terra (or similar), set up for orchids that like to be warm and wet. It'll have a fan for internal circulation, and ventilation to the outside, but should stay pretty moist at all times.

I'm still figuring out how much actual ground I'm going to have, but I'm probably going to have at least some dirt. Are there suitable mini non-epiphytes for this sort of terrarium? I know micro-mini sinningias exist, in fact I have some, but they need to dry out a little when they're resting. Unless people have successfully kept them damp at all times? I'd like to hear about it, if so.

I'm reading that a lot of the mini bulbos like to have their roots pretty much constantly wet. Has anyone ever tried to grow them in leaf litter? I'm curious if just placing one on the ground would work.

What are some plants that people keep with micro-mini orchids? I've seen an assortment of small ferns. Any suggestions in particular?

Can anyone tell me anything from personal experience about Begonia scutifolia/vankerckhovenii? All I can find is Glass Box Tropicals saying they like to be warm and moist. That, and pictures of some very cute little plants.