Change all bulkheads
Rinse the sand very well
Start curing rock now, don't push the install set it back a few weeks
Adding water won't add a spike, but the new rock/sand might
When I went from my 55 to my 120 it took me all weekend, I kept my coral and fish in rubbermaid bins with heaters, pumps but no lights. The corals will be fine with no light for a few days. Just don't rush it or get in a hurry, get it done right how you want it the first time. After RAP the club frag tank will be pretty empty so if you need me to hold anything let me know.
You'll need to test every day to check your parameters.