Its not the cruiselines that have weight limits on luggage, mainly the airlines. Just keep in mind, that any of your carry-ons have to fit through the x-ray machines before you board the ship, basically the same size as carry-on luggage you'd bring to fly. There may be times when you have to handle your luggage, so I'd keep the weight down to something manageable anyway, there is also no limit as to how many you can take onboard, unlike the major airlines.
Is this for a 7 day cruise? IF so, you should be able to get by with one piece of luggage per person and then a garment bag if necessary, plus any carry-ons.
Any locks you use should be of the type approved by th gov't baggage screeners. They have a master key to open them. If not the locks will just be cut off if necessary. If you are on a pre-cruise land package, pack a bag for the land part and a bag for the cruise. I think most airlines will allow two bags that are checked. That is what we will be doing for our Isand Princess trip in June. Our fifth cruise to Alaska.
Pack light, and remember to layer, and enjoy your cruise.