My suggestion would be (anyone else feel free to comment) to move at least half of your water from your old tank and add to the new.
2. Move the LR
/Sand to the new tank.
3. I would then add some premixed water (to the new tank), test and see what you have.
4. At this point, you should have an old tank with your critters in it and about half the water.
If you don't see any problems in your new tank, you have an easy way to catch your critters and move them over. If you keep the parameters in both tanks that same, you should be good to move the rest over, including the rest of your old SW
5. Just make sure you have extra water, for the purpose of a PWC