I'm impressed with the planted goldfish tank. I'm not an experienced vivarium grower, as I am working on my first one as well, but I would definitely let the plants grow for about a month before you put the frogs in so the roots can establish themselves. When buying the plants, usually pet stores have fairly small-sized plants for terrariums. I have found that Lowes/Home Depot have the same plants, but in a larger size, for a decent price. Starting with a larger plant will also give the plants the upper hand (at least initially). Obviously, just rinse all the dirt from the store off, and use your regular tank substrate. Plus, that month time frame allows any fertilizer that were used on the plant to dissipate. What to use to fertilize them once in the tank, I'm not sure. In addition to pythos, Bromeliads, Air Plants, Snake Plant, Ficus, and Creeping Fig are some other options that I have read members talk about frequently for White's.
Black Jungle Terrarium Supply - The Natural Choice! is a good website to look at plants. I don't necessarily agree with all their recommendations, but it will show you what's available. With a planted tank it is a good idea to have either a false bottom or a drainage layer (with LECA being the recommendation). Hope that helps a bit. I'd love to see a picture when you're finished.