The point about the overabundance of oxygen (from the plants) that would require venting, but limited nitrogen, which would ultimately result in suffocation is one of those great little details that you don't normally think about when you think about living on other planets. There is so much we take for granted living day to day on a planet that we've evolved in concert with, that it's easy to overlook the little (and big) details that are so important for life to exist.
This problem has been solved, and machines capable of separating gasses exist all over the world; they are commonly used in hospitals to provide oxygen to patients, and for various other purposes.[1]
