Wow that is a hefty price tag. I could think of so many vacations I would take with that budget.
We are family of 5 (3 kids 10 and under) who have done a trip similar but spent about a third of that. Things we did not go all out on. -
Went with a moderate.
Skipped the dining plan.
Stuck to beach days while on
DCL.
Skipped Hoppers
Whatever you don't miss DCL!!!
I couldn't agree with you more on this. That would be the very last thing to cut. Anyone who suggests cutting it hasn't cruised DCL.

It makes the parks feel like hard work! I would highly recommend doing parks first, then cruise. You will feel so pampered by the end of the cruise that the service in WDW will suddenly feel lacking. Extremely.
We just combined a WDW visit with a DCL cruise from Miami over Easter week. We rented points and stayed at BCV 2 nights.(later added 1 extra nt at WL.) BCV is a short walk to Epcot and easy boat to DHS. We feel that being on the Boardwalk loop around the lake has just as much Disney magic as being near MK. (and we have splurged on Poly before) If you've never stayed onsite, BC/YC/BW will still feel like a splurge. They're very nice and BC/YC share Stormalong Bay which is such an awesome pool. Poly has a lot of construction going on so I personally would wait until that is all done before trying there. Also maybe try it when you're not combining with a cruise.

(We stayed at the Poly with
free dining during Sept so it was as value-packed as a Poly stay could get.)
Plus from BC/YC/BW you can easily walk to the Dolphin where Alamo has an office in their lobby where we picked up a car to drive to Miami, one way rental. Just hold onto ALL of your receipts/paperwork for the car rental. Alamo has a free shuttle bus that will take you to the port but they do check all paperwork to make sure you had an Alamo rental that day. Right inside the lobby of the BC is Cape May Café which has a wonderful beach-themed character breakfast buffet. So we planned an early breakfast, (def. need an ADR) and walked out to our car plenty full for the 3 hr drive. You don't need to worry about getting a Sun Pass or having cash at the FL Turnpike tollbooths. Alamo has a device on their cars' license plates so it automatically bills your cc for all tolls + $3.00 per day that you incur any tolls. IIRC it was less than $10 for tolls. If you look on the cruise boards there's a Port of Miami thread complete with pics of the Alamo shuttle, how to navigate it all, etc.
I would also cut out the memory maker. CMs will gladly take pics with your own camera. I'd also cut out the hoppers. You could easily upgrade once you're in the parks if you feel like you can't live without it but honestly we only hop when our visit is less than 4 days therefore we need to combine 2 parks in 1 day. jmho
PPs are correct about having to budget for tips when using the dining plan. We tried the deluxe DP on this April trip and overall spent a couple hundred total on tips and it was only 3 of us. I wouldn't do the deluxe DP again. Way too much food and too much time spent doing TS meals.
Definitely count on $12 pp/day for the cruise tips, even for kids. They certainly earn their tips and we usually tip our dinner servers & stateroom host extra. With kids, they work even harder to make them happy.