This is the setup that is most appropriate for your size boat. The "tweakers" shown in red, are pulled on the windward side to change the lead angle to one more appropriate for a guy. It is a much simpler setup than running dedicated guys.
Most IOR boats I have sailed are not very happy with a symetric spinnaker and no mainsail, particularly if you are sailing deep. They tend to be more prone to "death rolls" which is when the spinnaker oscillates from side to side, causing the boat to roll side to side to increasing extremes. If the helmsman is not good at keeping the boat under the sail it can get very ugly! (It happens with the mainsail as well, but not as easily.) I don't mean to scare you, but you should be aware that is a characteristic of IOR hull forms!