The only thing I was warned about is that thinking in terms of time, say one year, one pennywort will spread out, propogate, and most importantly, fill in the top of the aquarium, which will choke the light to the rest of your plants. In my case this is desirable, since glass cats feel at home in such an environment (despite being south asian fish under a brazilian plant), and the rest of my plants are low-light creeping things, or are at least meant to be. Don't know how this fits into your plan, but no matter how big your tank, pruning will be a concern eventually...