I love the look of tall tanks! A large footprint (long and wide) is nice, but the "wow factor" of a 48" tall tank can't be beat. Maintenance can be a chore, but if you have the right tools, it's not so bad.
I have a 10' long x 3' wide x 4' tall tank and I love to see people's jaw hit the floor when they first see the tank.
My 2 cents worth of advice:
When comparing quotes, make sure that the thickness of the acrylic is clearly specified so that you can compare apples to apples. If one quote is significantly lower than another and the acrylic thickness is not specified, you can be pretty sure that the cheaper bid is going to cut costs by going with the thinnest material they can get away with. Since it sounds like you are getting estimates from the bigger players, they will likely use appropriately sized acrylic so this is probably a moot point. At 48" tall, I would say the absolute bare minimum should be 1.5" thick, although I bet the builders you are getting bids from would use 2" which would be even better. My tank is made out of 1.25" acrylic and the amount of deflection is a lot more than I'm comfortable with; in my opinion, it's definitely underbuilt.
I would suggest not skimping on the tank. Go with a reputable builder so that you know it's not their "first rodeo." I hate to even mention it with that beautiful looking floorplan, but that amount of water can cause some serious damage. Reviewing/revamping your insurance policy to make sure water damage is covered in the event of failure is probably a good idea.
I don't have too much advice in regards to the setup/filtration other than a comment on the pipes running beneath the slab. There is a guy here in Northern California with a 600G tank who buried his plumbing going out to a filtration shed in his backyard. His goal was to cool the tank by burying the pipes, but it works too well. His "geothermal chiller" works so well that in the winter his power bill to heat the tank is astronomical. In AZ, I'd imagine that you would want all the cooling you can get. I have no idea what depth would be ideal, but I'm just throwing that out there as something to consider; burying the pipes at X depth may save you some money on your electric bill.
Looking forward to seeing your progress. Good luck with your build!
(My apologies for the long post)