There is no limit to luggage on the ship. You will be issued 2 luggage tags per person, but can get more at the cruise desk of your WDW resort.
Luggage storage--in closet or under the bed (lift frame to slide under).
If you are driving, the amount of luggage probably doesn't matter to you; as above, leave the dirties in the car. If you are flying, I pack one "cruise only suitcase of stuff none of us will need at WDW. Then I do laundry on the last night at WDW (each resort has a laundry room, usually near the pool). Yes, it's easier for me in a
DVC resort. But it means that I bring half as many casual clothes, etc. Before luggage fees (or if on Southewst), we'd end up with 3 bags for the two of us--one cruise only, and one "each" beyond that.
Also, if flying, use the "musical chairs" packing system. Be sure that you spread out the clothing for each person among the bags. That way, if the airline loses one bag, everyone has something that they can wear! Put all your stuff in one case, and I promise--that's the case that gets lost!