From the research I did, the glass thickness all depends on the height of the tank. I just finished a 24x24x14 with 1/4" glass. If I had kids or a lot of traffic in my tanks area, I would have went 3/8 probably.
Although, I've put a straight edge on the tank when full and it wasn't flexing at all at the top so I think it was the best option for my build. I think they say 1/4 is good up to 15" and after that 3/8 is required, I didnt even check the next steps, but I think it increases every few inches. Try a few searches on google for more information on popular thickness rules.
Also, I went with a floating bottom and Black GE 100% Silicone II*.
Assembly is said to be harder but I found that to be untrue, with the floating bottom I will never have to worry about the stand being 100% level or putting a pad under it to prevent the bottom from shattering.