hey,
I did not understand whether it is that you are talking about FSSMC or the Forefront for Exchange (since you mentioned you only have one server you manage - I don't see why you need FSSMC besides reporting).
If you are talking about the FSSMC server, the traffic you can expect from it is while running any scheduled job that distributes templates/defintions/settings or collects logs.
the amount of data on those connections depends on the timing of the job (in case of defintions - if all engines have new defintions - it is possible that the update size will grow above the size your mentioned) and the amount of traffic going through your exchange server server that causes FSE logs to grow.
If you are talking on the exchange server, well I guess this one is obvious... traffic results from e-mail coming in and out and probably has nothing to do with the forefront on the server... :-)
hope this answers your questions...