also not an expert, just chiming in here...
i picked up 6 cobalt juvies last week. I'm trying to get a pair or two out of them. tincs are among the larger of the dart species and i think a 1 gallon is far too small for a pair of cobalts. from what Ive been reading the past few months, there is no species of PDF suitable for that size enclosure. there is a gentleman that has posted about his "5 gal hex" terrarium (looks really nice) project. people are saying that's even too small.
also, with a smaller viv / space, it will prove more difficult to control temperature and humidity than with a larger tank.
How I understand it- from researching the various PDF forums, a 10 gallon tank is the smallest enclosure recommended for any frogs and then, only a pair maximum.
About the plants: I use real plants. they look better. and when people come to see your frogs you can also show off your horticultural skills (even though it takes very little skill at all in terrarium setups)
I'm sure fake plants are fine, but i wouldn't want to have to worry about the metal wire that runs through each stem and leaf either rusting or potentially harming one of my frogs.
hopefully someone with more experience will confirm or correct this for you.