The rule of thumb that I have generally heard is, when you are finished packing, take half out. For me that approach was too general, so I started making an exact list of what I will wear each day, right down to socks and undies. For instance, I know that I am going to spend an entire day before dinner on the beach, so I plan to wear my swimsuit, coverup, sunhat, sandels, etc. Then for dinner, I am wearing a dress, sandels, light sweater, etc. I even include what jewelry that I am planning to wear. I try to "double-dip" where I can - same slacks with different top, etc. I include jammies, windbreakers and other things that I will need. This lessens the time that it takes to actually pack. It also helps keep me focused because I tend to pack when I am tired and not able to think clearly.
There is plenty of room in the closet for suitcases (we fit our Owner's Locker in there with no problem), as well as space under the bed.