Let's talk upgrading tanks - Will be upgrading a 46 to a 90 and need some answers

We are looking to upgrade our 46 aquarium to a 90 very soon, and have a few questions. The 46 gallon is very well established at 5 years old, and includes various corals such as montis, a giant duncan, brain coral, acros, and mushrooms. We currently have a pygmy angel, ocellaris clown, yellow watchman goby, six line wrasse, candy hogfish, and two pistol shrimp and some various inverts like serpent stars and brittle stars. We have roughly 70 pounds total of live rock between the display tank and sump, and 50 pounds of sand. Hopefully that gives you a sense of the ecosystem here. We did have a 6 bulb T5 running until my mom got skittish of the hogfish potentially jumping (he's new), so she slapped our old sundial 4 bulb T5 on there and stuck my DIY canopy on it again to contain him. This setup should just be temporary until the new tank comes along.

We are running an older Reef Octo 150, and just have a bag of carbon and a bag of just phosphate remover in the sump, and that's it. Everything goes down through an overflow box (siphon), trickles over some rock, gets skimmed and flows through carbon and the phosban stuff, and then pumped back up. Simple.

This 90 is going to be anything but simple compared to our existing setup.

We will be getting a drilled tank (no experience with drilled), and I am interested in making my own sump using a pre-existing tank with me installing acrylic baffles for chambers, with a skimming/hardware section on one side, return pump in the middle, and refugium on the right.

Any tips or suggestions would be fantastic, but we do have a specific set of questions for things to start off with.

The first involves just a general transfer from tank to tank. What should we expect? Is it really just "remove rocks, water, and fish into plastic tub, set up new tank in position, fill new tank with base rock, dead sand, and then established tanks live sand, live rock, and fish and add more water, then you're good to go"? Or is there more to it? Should we expect a mini-cycle with this larger setup? Will the tank go through some growing pains again, such as the hair algae we had for a while in the beginnings of the old tank? I'm assuming we will need to mini-aclimate the fish to the new water to be safe?

Next comes some plumbing questions. The return line is simple enough to grasp, I think. Slap some pipe on a pump, let the pump flow into the display tank, and preferably stick a valve or hole on their to prevent back-siphoning. The drain line to the sump is what is puzzling me. Do drilled tanks still use the "hook" or "candy cane" shaped overflow pipe that old tanks used to have? Or does the water just cascade into a hole? I've seen both, and I'm not sure which is preferred today.

Also, why the flip to people have ball valves on their drain line? I see that often, and as you can probably guess, ours does not have one. I'm not quite sure what it's use is. Our flow is always regulated by our return pump, no ball valve required. We are planning on sticking a T-into the drain line and letting that control the flow of the refugium, so is that what ball valves are for? To help regulate flow with situations like that?

Thirdly, how do I properly cut acrylic and glue it into a glass aquarium? I considered just cutting it on my table saw and using silicone to stick it in the sump to prepare the different compartments, but I'm not entirely sure how smart that would be or if it's the right idea at all.

Do we need to consider various reactors to add to the sump, rather than simply sticking carbon and phosban in a bag and using that?

Also, this new aquarium will be almost double the size of our 46. Do we need to consider reinforcing our floor to hold it, or should everything still be ok? It is not on an external wall of the house, it is on an internal wall, but the floor joists do run in the appropriate direction to help distribute weight. We were considering placing a base of plywood down larger than the stand itself to further distribute weight over the floor, is that a good idea? And we remember a trick where people place foam under their aquarium to help level it. Is that trick still used? What kind of foam do you use?

Thank you, and any feedback is appreciated.