The vancouver aquarium would be the closest Aquarium you could visit with a monster tank, and monster fish.
Agreed that the pH is not a big deal, and I wouldn't try to mess with altering it. Set yourself up an automatic waterchange system on float switches, you'll thank yourself later.
Are you looking for that peice of acrylic to be the entire front viewing window? Have you ever considered re-thinking your idea, and making the 'viewing' window possibly smaller then the dimensions of your tank. This way you would not have to have a single sheet of acrylic, seemed togethor at the corner, supporting 1/4 the tank. Especially with a tank so tall. I would go with a 10' viewing window, and build a frame around it out of other materials.. or you could do two 6 foot viewing windows, with a center brace..
I know a person here who works in the acrylic business.. He was looking into building tanks, and was rambling off some sizes he can get. The largest he said he could get was a 14'x8'x2" sheet, I think. I will ask him next time I see him..