The thing I've learnt with this is sort of sequential planting. After I added moss to the wood and let it get well established, I could then use it as a substrate to tuck other stuff into.
There's a wide variety growing in the big mass, hydrocotyle obvs, crypts, buce, pinnatafida, s. Repens, zosterfolia, rotala etc
I've half a plan of what I want to do next doing the same sort of thing. But for that id need to take this down, and that feels like a big step!