To plant or not to plant - that is the question....

I've ordered the heater and sponge filter - getting the 15L tank today. Will be dividing it into three compartments in order to attempt to breed bettas.

Now, I have a choice - to plant or not to plant it. I do believe in and love my planted tanks - and feel that they would help balance this system and give hiding places for the fry. I have a couple of options:

1. Create walls of baby java ferns on the two dividers - keeping the bottom of the breeding tank bare.
2. Lay tiles of growing mosses on the bare bottom
3. Fully planting the tank using proper sandy substrate and plants such as microswords/mosses.

Water level will only be 4" at first, then 1" added per week as the fry grow - until tank is fully filled. Will be using 'mature' water from my main planted tank to ensure its cycled.