Yes height plays a major role in glass thickness.
Do you want rimless or eurobraced? on that size, 1/2" glass rimless 3/8" eurbraced
Kelly's Stained Glass in Ogden does good work and has very good pricing on glass (even starphire)
Use a quality industrial grade adhesive silicone, Momentive RTV 108 (clear) or 103 (black) this stuff skins over super quick so you have to work fast, but its psi rating is very high compaired to silicone you will find at a big box store. I have also heard Dow Cornering 999 works well, but I don't have experience with it.
I would recommend a small eurobrace around the bottom of the tank for added silicone surface area. IMO 1/2" is not enough silicone area to hold on the bottom of the aquarium. Most of the pressure is at the bottom (well at tad above the bottom
) on that size tank its not exactly necessary, but most do the bottom euro after you get past 100 gallons but I would rather be safe then sorry, its cheap to do.
hope I helped answer some questions for ya