Recently moved a 75g across town so sort of similar deal:

-at new place was able to make up 80g of SW, heated and aged for 4 days prior to move
-moving day, placed LR in two large tubs, covered in water
-mushrooms in a pail
-saved 10g water in pails
-placed fish in a 5g pail
-sadly dumped the whole DSB
-drained the tank, scraped of all the feather dusters, rinsed in FW (probably what kill the Coraline on the back glass, hindsight, should have cleared it all off)
-moved the tank etc
-at new house, placed in LR
-added original 10g of water back
-topped with SW previously made
-drip acclimatized fish/shroom, placed in tank
-top tank back up with aged SW

Had planned to keep the top 1" of DSB for seeding in a 33g for a new system I'll be setting up but didn't get it re-caulk in time for the move. Plan was to move the tank keep the LS with PH, heater, once new system up, setup a DSB in the refugium then top with the LS.

Since my current system is just temporary, running it BB. If I was going to keep the 75g, would probably have kept the top 1", moved as above, add new rinsed sand, top with saved sand, add LR, water etc.

if i where u i would just chuck the sand, get new sand then its clean and you wont have to worry about the nutrients in the old sand.