Yes they will eat your plants (At least in my experience they will).
Also, might I point out that your Serpaes may have a change of nipping your 2 Gouramis - Just sayin'.
Actually, I think it depends on whether you can keep the Serpaes and Red Eyes in the same tank with longfinned fish - it really all depends on the personality of each individual fish.
I have successfully kept Red Eye Tetra with Angelfish before. No nipping. School of 8 when I did.
Truthfully, it depends. I still advise against it. IME, serpaes are usally nippy no matter what. But, some people have kept them without an issue. If you want to try it, go ahead. Just be very watchful. I personally would try the red eyes long before I would try the serpaes. My red eyes were pretty nippy. Once I moved them to my angel community, the actually left the angels alone, but harassed the rummies and platys like mad. In a different community, they harrassed my silver tip tetras and a betta. But like I said, I would still give them a shot with a gourami before I would ever try a gourami with serpaes. Up to you though. Fish don't always do what we think they should do.i'm doing schools of 10, shouldnt that help them to keep the aggression amongst themselves?