Lovely rockscape! Can't wait to see it planted.
Are you looking to be geographically "accurate" for your frogs? If so, knowing what region the frogs come from would help in suggesting types of orchids that would be "right" with them. That said, wood frogs here in PA seem to enjoy sitting on the leaves of phalaenopsis!
I never used to do much mounting until I got a large wardian case. (I don't have a greenhouse.) Now that I can keep the ambient humidity up, I'm finding I really like both the look and ease of care that comes with mounted orchids. You obviously won't have problems keeping up the humidity -- but pay attention to air movement, too. If you don't have "lively" air around the orchids, you'll run a much greater risk of developing fungal problems with the plants.
Good luck!
LP