That plant that is growing fast is hornwort, it grows like that in just about every setting. I wouldn't worry about that featherfin bothering your tetras or plants. He might uproot a few but no biggie. The only thing I would worry about is other bottom feeders, he might be aggressive towards smaller ones, such as cory cats or kuhlis. The only other bottom feeders I have successfully kept with my featherfin are clown loaches, pictus cats, and plecos, but all of those are no bueno in a planted aquarium with small tetras. A bristlenose, clown, and rubber lip pleco are exceptions to that though.