You can leave the Passport field blank. Just make sure your birthdate information is correct so they can match it to your birth certificate. I completed this on the Cruise Personalizer and the next time I checked, the wrong month was showing.
Yeah if your going on Princess. You need to pre register 60+ days prior to departure to avoid immigration check in. Last time we went we registered45 days and couldnt do the express check in. so do it today!