I have a somewhat different view on the matter:
I have seen many dart tanks with water feature areas, most small and some rather deep... so perhaps a reasonable concern is the amount of surface provided that will aid the frogs in their attempts to get out of the water (ie: wood, rocks, etc). For a tank with as much floor space as a 40 breeder, a water feature won't detract from the usable area too much, imo. I agree that a false bottom will work well, plus LECA clay balls are an expensive alternative.
For lighting, I have found that the majority of terrarium plants will thrive given greater amounts and that compact florescents are superior in this regard. The amount of footcandles produced by power compacts is significantly higher than that of t8s or t5s. If your goal is only to grow some moss, philodendrons, and rabbits foot ferns that won't need much light, then perhaps less lighting would be sufficient and a better choice, but as I mentioned, many terrarium plants will appreciate higher lighting. So, I recommend looking into all the plants you might want to stock the tank with and then researching the appropriate light and moisture for all that you might be better able to select a light fixture and bulbs and also know where in the terrarium the various plants will do best. Many of the plants will be coming from very different enviroments, such as forest floor, canopy, the side or branch of a tree, cloud forests, etc - some will want a bright/dry spot (high in the tank), some a bright/wet spot, some a shady/wet spot, and so on.
There are many places to gain more insight into terrarium plant and dart frog husbandry - I like www.denroboard.com
- it has forums dedicated to frogs, their health, plants, terrarium construction, and more. The vendor links there can point you in the direction of some very nice plants that are terrarium worthy, as well. I hope this isn't tmi.
Best of luck,