A great start! My first thought was that a nice reddish stem behind the driftwood would look good. You mentioned Rotala Rotundifolia, which is a good choice. If it were my tank, I would start by sloping the substrate a bit towards the back left corner (this will raise the driftwood a bit and give a greater sense of depth).
Then I would plant the following:
Anubias nana petite, hygrophilia pinnatafida, or bucephalandra on the driftwood. These are nice for tying onto driftwood/rocks since they do not need to be planted in the substrate.
Some sort of stem behind the driftwood (rotala or similar).
I'm not sure what type of plant you already have planted, but it would be good clumped around the base of the driftwood and along the back of the aquarium interspersed with a med sized cryptocoryne.
In the foreground I would go for an easy carpet plant (I don't know the specs of your light so that can rule some things out) such as a dwarf hairgrass or a micro sword.
Either way, you are off to a good start and have healthy looking plants already!