[asylumdown]

I would keep your current tank running completely as is.

Then, I'd treat the big tank as a completely new setup, as though you weren't doing a transfer at all. New sand (it's never worth the problems it can cause to try and save old sand IMO), whatever new rock you were going to add to make up the balance of what's in the old tank, then fill it with completely brand new salt water, matched closely in salinity to your old tank. If you're using mostly dead rock like marco or pukani or something in the new tank, you can do the majority of your aquascaping before you fill the big guy with RO water and mix in your salt. If you're using actual live rock, you'll obviously want to wait until the tank is filled with salt water. Make sure to leave allowances for the amount of rock that will eventually be transferred over from the little tank in your scaping.

Now you'll have two completely separate systems running simultaneously. If you've stocked the big tank with live rock, you'll want to monitor it over at least a week to see if there's a cycle, and if one happens ride it out as you would any other new tank. If you've used all dead rock, I'd just wait a day or two to let things settle, the water to clear up, temperatures to stabilize, etc.

Then I would do the transfer. Assuming your big and little tank's temps and salinities were closely matched, I would first remove all corals and rocks from the little tank and place them in your big tank wherever you want them. I personally wouldn't bother doing any sort of an acclimation, but perhaps I'm harsh. If it makes you feel better you could maybe drip acclimate them as if you were bringing them home from the store new, but I don't think there will be a difference in outcomes either way. Then I'd catch my fish, and move them over. Then I'd discard 100% of my old tank water. I personally see no reason to hang on to it or try and save it as there are plenty of tanks that get 99-100% water changes on a routine basis and thrive and it's more trouble than it's worth for what will likely be no more than an incredibly minor and short lived difference.

Then your old tank is no more. For the following week I'd monitor for ammonia closely. Moving your rock this way should have brought the majority of your filtration capacity with you, and you've got the same number of fish per pound of live rock as you did in your small tank, but in a much larger volume of water. However, you're losing the nitrification capacity of your old sand and any surfaces in the actual aquarium itself that bacteria had colonized. If you see a cycle at all, it will probably be very small and easily managed with a product like prime and water changes.