I want to add some tall background plants, thinking either Water Sprite or Cabomba. Think about your temp of water? WS is fine for almost all temps but I have bad kharma with Cabomba and anything over 75. M.O.P.E.
I also wanted to add in either Eleocharis or a Micro Sword. why not both?
I might be re-arranging my hardscape to better suit the potential takeover of the grass.
One question on that, would the loaches get upset with a grass covering of the gravel?I see a Chinese Algae eater, what type of loaches are in there?
Hardscape looks fine unless you have something really different about it for your taste in mind.