I've moved my 75 gallon twice. I'm in the middle of buying a house and will be moving it again soon. It sucks lol, there's no doubt. The most important part is keeping your LR
wet. If it dries out you're in trouble. You could definitely use that 55. If it were me, I'd set the 55 up out of the way (but close to where the 75 is going) at the new house, transport all your LR
in buckets of tank water and put the LR
and the fish in the 55 with a powerhead or 2 until your 75 is setup. Using ALL the tank water from the 75 however isn't a must, its the LR
that holds all the bacteria. I would also recommend buying new LS
and seeding it with some that's in your current tank because as stated if you disturb your sandbed it will probably cause a spike and mini cycle. As long as the distance you're traveling to the new house isn't too far the fish should be ok without an air pump. You might want to enlist some of your stronger friends or relatives too lol. Good luck.