Some suggestions: if you have the funds for personal guides, you can, of course, get them. But that's a might pricey undertaking and sometimes even the guides that get good reviews online can be dull or uninformative. It's less of a risk (financially) to do a small group tour and you can find those through such companies as CruisingExcursions.com or ShoreTrips.com. Or pick up some e guidebooks and simply hit the sights on your own. You can do so in many of thse cities. And you'll find complete reviews of the highlights of those destination on this website, so you may want to start your research there.
I hope this has answered some of your questions. Really, a lot depends on which sights most interest you, since these port stops are so rich, and sometimes your time is limited.
On the question of checking in to the boat first: I think that would be a time waster. Find a hotel that will hold your luggage for you, explore and then make your way to the boat a few hours before the sailing (most will have specific times that you need to check in by).