We've done land, sea and land & sea and we don't be doing a land & sea again (at least not with
DCL). First off, the shorter DCL cruises are probably some of the worst values so it makes it really expensive. There are positive to doing land before and after your cruise but pick whatever suits your schedule better. Some people want to relax on board after a few hard days in the parks but on shorter sailings some people end up waking up earlier on the shorter sailings because they don't want to miss anything on the ship and with fewer days you've got less time. Some peple will use their FP to rest a little on park days but be up at 7 am every day on the boat and some people will do the opposite....there is not one portion more relaxing than the other. It's all in how you approach them.
My suggestion would be to first chose the amount of time that you have and find the best itinerary/cruise that fits that schedule. If DCL is not 100% a must do consider other lines sailing out of Port Canaveral or Tampa. Once you've identified your itinerary then plug in the days at parks that are going to offer the most opportunities to experience the lowest crowds.
Do not do DCL transfers...rent a car to drop off at the port then rent one to pick up at the port after the cruise. Its going to give you flexibility and for a family of 4 you can find a small SUV for around $125 for each one way trip. You can pick it up and drop it off either at the car care center near magic kingdom or at the Swan and Dolphin.
Be prepared for an expensive trip. The cost of a DCL 4/5 night cruise is as much or more than what a week cruise would end up costing you on other lines, then by adding in park tickets, resort stays, food, etc the costs start to add up. Disney becomes a better value when you go for a longer time because the
ticket prices drop so if you have another trip within the next year in mind you might want to consider APs to drop the cost down over the long term.
