Regarding your vals and excel, I started overdosing my tank with excel to get rid of some nasty hair algae, and while I lost quite a lot of val leaves, I'd say that 75% of the leaves were fine (I have about 20 val rosettes in my tank). Now that I'm dosing normally with the excel, the plants are fine and growing well. I think they might just need to build up a tolerance, and I think some varieties might be more sensitive than others (mine are corkscrew).
Can I make some suggestions?
1. I'd veer away from a java moss lawn. Something like riccia would look much prettier. For a lawn, you probably wouldnt want to use the more expensive mosses (xmas, flame) either. Were you planning on using screens or typing the moss to slate or rocks to create the lawn? Java just always looks messy to me.
2. I think the little "scenic" scape might be really nice here. Its small enough that you can make a tiny white sand river, rock mountains, sticks for trees, what have you, as long as you're comfortable working on such a minute scale. And its so small with little investment in raw materials, you can just turn it upside down, shake, and start all over if you want to.
3. IMHO, small leaved-plants always look best in nano tanks. Large-leafed plants will make the tank look cramped and take away from the "hills and valleys" scene you described.
I think this little tank has a lot of potential.