Hi
I can't give much information on bracing, but I also have a turtle tank which is a smaller which is 1200x45(h)x38(w). It is made of 6mm glass.
On the top of the tank, it has a centre brace approx 20cm wide, and one brace on each end about 15cm wide
On the bottom of the Tank it has end braces and front and back braces.
HTH