In the wall!! Jeez that's going to be a project! Get as many tanks and containers with heaters, blowers ect,.. as you can too. You can use them while moving things around,. It will come in handy. I would also pick up a new large trash barrel to make a bunch of water,.. You will need a lot over the next few weeks. A tarp will help when cutting the adjustments in the wall preventing things from getting into the tanks. When moving tanks,.. I take some water from the old and place it into two containers,.. I take the live rock and give them a little shake into the first container to remove detritus and then place then clean rock into the second container. I let the first container sit then at night I go hunting with a flashlight and turkey baster,... and collect as many little creatures as I can and place them into the second container with the liverock. I do the same process when I clean out the sand, which is a little more of a process. I use egg crate zip tied together to make a very large frag rack too,.. It helps having that in a container/tank whiling moving because you can easily put corals and frags aside while working on the aquascaping. A few things that may help too,.. Coral dip,.. Adhesive/putty for liver rock,.. A six pack and friends willing to help.
Good luck!