I'd consider using as much of the water as possible just to help with stability.I think I will transfer over immediately. From what I've been reading and everything, I shouldn't have much of an issue doing it that way. Should just be able to transfer all my rock over, and that will continue to be good enough for my current bio load. I will probably add some more rock, since this one is bigger than the 65-gallon.
Going to get all new sand and rinse it very well, then I'll fill the tank with new water. I'll use some old water from the tank also, not sure how much. Going to scrub and clean all my rocks really well also and rinse them in the old tank water. Hopefully that will help with the GHA that is in there from spreading to much to the new tank. I'm hoping to transfer it all this week but may end up being this weekend depending on what all I get done.