My Alternanthera Reineckii gets crumply often, even in SMS. Seems to respond to all kinds of fluctuations including ferts and CO2, but the good thing is you can always clip the tops, discard the bottoms, or hide the bottoms with mid ground plants.
You probably won't experience too much nipping from the danios until you have them around fish that have graceful, threaded fins, like angelfish. With angelfish, seems like
every schooler becomes a nipper, the fins are just too tantalizing.
The tank looks good so far
I agree you should play around more with the rocks to get something less manufactured and more natural looking. Maybe group them in the center with all your branches radiating out from the mass. I'm not a big fan of the straight branches though, I much more prefer your slimmer, branchier piece on the mid right side, a group of those coming from a cluster of stones could look very natural and draw the eye in.