Should we include a guest?

In our case, for the people we know that don't have a steady significant other, we invited solo. I cannot tell you how many of these people have either replied "and date" or have called me or my fiance personally to ask why they can't bring a date. It's gotten to the point where I just wish we would have allowed the guest to save the grief. In your case, you may have an easier time with it since it's much smaller and you can personally spread the word. For bigger weddings, I don't necessarily recommend it.