Your tank is amazing, I hope I get pieces of wood like yours one day.
About Echinodorus tenellus, well I have it.
It's under 1.5WPG T5HO (30g tank), I started with two plants, of course it took quite a while to settle in.
It's been in the tank since Mid-Jan and I already have 4 more plantlets and I don't even dose ferts or co2.
Hopefully when I introduce dry ferts I will rapidly gain a carpet.