You can do "outdoor" electrical connections and use outdoor light receptacles that do not require a full roof. I don't know about the ceiling fans. Perhaps they make rain-proof housings for some?

If you do run electricity, then you have even more options. You could even do a retractable awning style roof. Make the dock have nice amenities when people are using it, and then hide part of the structure so that storms have less to attack and destroy your dock.

Have fun on your designs. You have nearly endless choices for your project.