Welcome to Cruise Critic and the rabbit hole (or should I say money pit) that is cruising. I would add that a couple of weeks to the Canaries on Iona, although nice, will not really give you any idea of a world cruise on say, Arcadia. The ships are just too different, not just in facilities but activities and space. On a world cruise you usually have up to 6 straight days at sea crossing the Pacific. There may also be days when the seas are rough, which you might not notice on a ship the size of Iona, but will feel different on a smaller ship. On the other hand, 3 months at sea, visiting wonderful far-away ports is fabulous. I would suggest 2 weeks on Aurora or Arcadia first to see if you like those ships and save Iona for other cruises.