a 50 would be large enough IMO but that can depend on stocking also. glass thickness will depend on dimensions. make sure it will fit throught the doors you need it to. and give yourself some wiggle room. I am building mine to be 6'x3'x34" tall there is a glass thickness calculator in the stickys at the top of the DIY section. thewre is also an Acrylic thickeness calculator there. check out your glass prices for the different thicknesses also before you start construction. some places try to rape you when you look for thicker glass which can add a big cost to the tank. Glass is cheeper 99% of the time but Acrylic is a bit clearer but scratches easily. good luck with the build