Cellcast acrylic is soft. It bends with ease. Your height isn't bad. Do you plan on running your tank with water to the top or down a couple inches? Something to consider...
There are a couple of acrylic calculators on the web, DYI Guy from YouTube has one.
Your top and bottom pane can be 1/2", I can't speak for your 7ft length vertical panels though. When I researched mine, before I started my design/build, I found a few guys that went thicker on the sides and never regretted it. It's the distortion in the material bending that can cause hazing along with the slight fishbowl look.
Your going to gain so much from strength and clarity.
