As an experienced mechanical engineer I build a lot of things. Big budget stuff at work and small budget stuff at home. Frankly, with questions that fundamental, I would never attempt a build that critical without serious, expert help.
600+ gallons of water will not only destroy your home, but it could serious injure or kill a person if you had a failure. Not to mention losing many thousands of dollars. Not only do you need a professional to build the tank, you need a civil engineer to analyze the support for the tank. At about 64#/cu
-ft, you're supporting an enormous weight. Your home insurance policy will need serious restructuring as well. Sure hope you don't take this lightly.