It dosent have to be too wet for springtails to survive, the leaves will help increase the humidity locally which should be enough for them. I wouldn't expect the population to explode though, they will subsist given the right conditions.
In terms of your Isopods, are you going to use dwarf whites? (T. tormentosa) these guys survive best and are the bet producers, my recommendation would be to split the culture, half in a viv and half kept for future vivs. These guys will keep the viv clean and will explode under normal phelsuma viv conditions, the population will at least double each month ( perhaps triple it will depend on your temps and feeding regime). To give them a good start I would use some fish flake or oats as a food source for the first couple of months, you will find they swarm around this whilst they are building numbers, feed a little, if it moulds over, fine! Both the Isopods and the springtails will eat the mould.
Good luck and keep us updated on your progress
Ben