I'm not a fan of Glow-Shift but I had a set of Auto Meters and they looked very close to stock in the day time and the green LEDs made them look great at night. Many folks asked me if they were factory.
EGT should read up to 1500* but you never want to go above 1200* for more than a few seconds.
Boost depends on what power levels you're looking for. As a general rule, you need 1 psi of boost for every 10 rwhp so if you're not going up past 350 rwhp then a 35 psi gauge should be fine. However if oyu plan on doing major mods to the engine and drive train and want huge HP, go ahead and get the 60 psi gauge as it's cheaper to do it once and be done with it.
Trans Temp should be a standard gauge. I think max should be about 250* but I've only had a Duramax with the auto and the rest of my diesels have been bolt actions and trans temp wasn't an issue with me.