Hi, I am now gathering plants and so on for a 75 gallon plaudarium. It is to be at least half way full of water. One problem is that as it is a fish tank and not a case made specifically for terrarium/vivariums, I have the problem of not so much room for plants at the top. My plan is to eventually create a kind of "top" which would be something like a wardian case. This would raise my plant count.
As far as low light plants that love being in a humid environment, grow slowly, remain small, you can not go wrong with small mounted orchids.
In addition I got several varieties of spike moss, and a few low light plants available at garden centers.
I did consider orchids, but having no experience with them, and not knowing what I was getting, I decided to hold off. Maybe another time if I've got someone making sure I'm not doing dumb things to them.
I did figure out a solution, I'm not sure how it will work out long term, but for now, it seems to be working. I got a plastic drawer organizer basket, and it turns out it fits snugly between my tank and the wall. A bit of light adjustment later, and hopefully it will work.
I added a layer of gravel to the bottom (drainage/holding some water), and used some rampantly growing local moss to line the inside. I used dirt from the plant pots to fill it. I added a Lemon Button fern (split in 2), Purple Waffle plant (2/4 plants in pot), and two reaaaally small cuttings from a Rex Begonia. No idea what will work or not (though I'm confident the fern will survive at least), but it's been a couple days, and things have only needed water once. To water it, I took the basket to a sink, and gave it a drink. I let it drain for a bit before replacing it.
The basket slips out of its little hole quite easily, so I'll probably add a couple nails or something to make sure it doesn't fall.