20G terrarium plants

[harpspiel]

I'm planning to start up a terrarium - a tropical set-up, 20 gallon tank, mostly orchids but a few ferns and other plants. The problem is that some of the orchids really need a dry/cool period to flower, and others don't. I'm wondering if the warmer-growing orchids can tolerate a cooler and drier winter period (for instance, around 65-70F). Here are the orchids I'm considering:
Dendrobium aggregatum
Haraella odorata
Ludisia discolor
Mediocalcar decoratum
Phal. schilleriana, violacea, or other small phals
Paph delenatii
Bulbophyllum frostii x dentiferum

I'd really like a phal species and a paph/phrag species, but if the ones I've suggested aren't suitable and there are better ones, that would be great to know too.

Also, I've been having a hard time finding out sizes. If anyone knows that certain of these are too large, I'd be happy to know.