wow, that's a lot of questions. i'll try to answer them, but i'll probably miss a few....lol
you can do an island tank very easily and cheaply. i actually designed one to go in a 40b, but never got around to building it completely. go to the dollar store and get a small plastic wastepaper basket. trim it to about an inch above your planned water level, fill it with a drainage layer (don't forget a drainage tube) and the substrate of your choice. it will actually be small enough that if you so choose, you can use gravel as a drainage layer. place that in a spot in the tank that you want it, and you have an instant island. trim it with some moss and plant some aquatics in front of it and no one will be the wiser. of course, you can still do egg crate easily enough. the way i described is just a very economical way of doing it, and it will keep the substrate dry.
a cfl rated at 6500k will provide sufficient lighting to any live plants you may keep in the viv, but will provide only the slightest amount of heat. the only heat will come from the attached ballast, not from the light itself, so you may want to plan for a supplemental heat source. as far as uvb lighting goes, it's not really necessary, but if you feel more comfortable having it, then by all means go for it. none of my tanks have uv lighting. they all run 6500k florescent lighting.
louis already covered the cleaning of coco fiber, but keep in mind, that phat phrogs require monthly substrate changes, but many other frogs do not, especially if you are keeping a live vivarium. with the addition of microfauna as a cleaning crew, you can just spot clean and do annual substrate changes. but as Louis said, the nose knows
keeping a springtail culture in the tank as a primary food source most likely will not work. the frogs will diminish your culture very quickly. your best bet is to seed the tank with microfauna first, then wait about a month for them to populate the tank before adding the frogs. give them some time to establish themselves before adding the murderers....lol feed fruit flies as a primary food source, and they will snack on the springtails in between meals. the springtails just won't reproduce fast enough to keep up with the frog's appetites. the frogs will eat until they explode, if given the chance.....lol as far as rice flour beetles, i would only feed the larvae.
hope i got most of your questions answered
