Hmm, replacement for Hygrophila difformis? Hemianthus micranthemoides, Rotala rotundifolia "green," and Heteranthera zosterifolia would all be excellent choices.
Mayaca fluviatilis is also a very pretty, although common plant, with bright, lime green foliage. It acts as a weather vane for proper trace fertilization -- if the tips go white, you are not adding enough iron/traces.
Don't know about the moss. Is the E. tenellus sending out runners yet?
If you want you moss wall to grow out faster, try thinning the moss out a bit more to the point that no frond overlaps another. From the looks of it, you should be able to spread out what you have to cover practically the 2 plates you are using. This will maximize your moss, allowing all the tips to get enough light. right now, everything you have that is being shaded will not grow as fast (if at all) and is essentially wasted.
As for your H.difformis, you might want to think about swapping some with a grass type plant like c. helferi, Vallineria, Sagitteria, crinum, even narrow leaved forms of Echinodorus (E. uruguayensis, horemanni, narrow leaf red rubin etc.) I have always liked the use of vertical lines in a tank that has Nymphaea, makes for a great counterpoint to the big wide lilly leaves.
the e.tennellus is throwing out runners already, but the leaves seem to be growing longer and faster than the runners, and i find that pretty weird.
not much difference for the moss, i think i'll heed aaron's advice and do the single frond planting, but that'll be after my exams. :wink: do moss need lots of light? because if i were to spread it, those lower down might not get much light due to the other plants blocking the light..