Hey Ashley, I just did a transfer of a 20g to a 40B. Had 22lbs of live rock (LR) in the 20g. Problem is I got some aiptasia. So I was not going to transfer that over. What I did was add 20lbs of new live rock. Boiled and baked the old 22lbs. (DO NOT DO THAT EVER IF YOU DONT KNOW WHAT YOU ARE DOING). Had to add that before everyone jumps down my throat.
First off. I want to say nice old tank. Paint the back of your new one. Hides the chords and equipment. Plus no salt creep will show. 5 coats of black is great. Use a sponge roller and non toxic latex paint. It will pop your fish and corals that much better. Plus if you don't like the color. Scrape it off and add one you like. White is very different. I have a marine blue on my brackish tank.
I bought LIVE Black Hawaiian 40lbs and 10lbs aragonite. Stable pH. Give it a nice salt and pepper look.
Put new 20lbs LR. Soon to be 42 total. 1 lbs per gallon. Good rule of thumb.
So for the first 3 weeks. I cycled my tank with just sand, LR, Aqueon Pro 150W Heater, MJ1200, and FLUVAL C4. 14g of used tank water from the 20g tank, and new saltwater. Poured that on a bowl inside the tank so it did not kick up the LIVE sand. Yes some will and it will stick to the side of your tank, because of it being magnetic. The water from the 20g tank was not agitated. Didn't want to add any aiptasia. Next, Bought a table shrimp from the grocery store. Tucked it in the sand bed and let it rot. Fed the tank a little bit of each food that I use to feed my fish every few days of something different, but not a lot. Basically to get my tank/bacteria to know what to break down. Ammonia spiked. Nitrates spiked. Nitrites spiked. Pulled the rotted shrimp and scallop slices out. Did a big water change. Let it balance for a few days. Ammonia 0, nitrites 0, nitrates 0. Tank was cycled. Pulled all the live rock from the 20g. Put all my corals, 6 fish, fire+skunk+peppermint shrimp, 4 crabs, and tuxedo urchin in the 40B. I will say everyone is happy, corals are booming and growing onto the LR. Slowly putting in the OLD LR that I nuked and cycled every other week. I feel your worries. You don't want anything to die. Anytime you do a weekly water change when your tank is cycling. Pull say 10g from the new tank. Dump it. Pull 10 from your old tank. Put that in the new tank. When I felt good about it. I had both tanks pretty much identical. Netted the fish and put each one in. Don't be so gingerly catching the fish. You don't want to chase them so the are so dead tired and stressed out for an hour. Corner, capture, net, boom put it in. The tank is all set for them. Light off to reduce stress and a light feed to get them to understand everything is going to be okay after today. Do it during the day so they can find a descent place to chill and figure out if sleeping there is going to be good for them. Keep like a moonlight on for them. That's my 2 cents. Here are some tank pics. This is all since January 2017