I thikn one would be fine. They max out at about 4" in all actuallity. Also, being labrynth fish, they are not as active as most other fish. I have two and am quite familar with their behavior....but either way, I'm not going to get into a gourami debate when the guy hasn't mentioned what he's gonna do about the two rams
Also, i'm not suggesting he still get the tetras and cories with the gourami....