Stock the tank with springtails and/or sow bugs. They will work away and the stuff you can't find. With a healthy little micro-ecosystem you should be able to go months or even years without having to do a full breakdown of the substrate.
That's awesome you can have some experienced in person guidance, suck as much info out of them as you can. Since they don't know frogs make sure you look into the frog safety of any plants your friend recommends, and of course post pictures after the remodeling!