So I am tentatively planning to stay in Rapallo, but want to visit the Cinque Terre area and possibly other areas north of Rapallio by ferry. I found one ferry online -Traghetti - and am waiting for info as to when I can book for May. Does anyone have information about this line or any other that you have used?
This is the primary ferry company serving Rapallo, which you probably saw earlier: http://traghettiportofino.it/en/. There's not much schedule selection for making the trip you want and I think also not much competition. If only one direction timing suits your schedule, you could always take the train the opposite direction (but no train service to/from Porto Venere, if you go that far).
Within the Cinque Terre, you might switch over to using this more frequent boat service: http://www.navigazionegolfodeipoeti.it/en/timetables-and-rates.html.