aquarium size

So I am shopping around for a new reef tank and I really like a 90-gallon thats 36 x 24 x 24. I know anything beyond 24 inches tall can become a hassle to clean, but I was hoping you guys could give me some pros and cons to getting a tank that size that I haven't already considered. Any feedback...

Is a 32g cube too small for a Cherub Angel? I love them but only want to own one if I can give them a good home. It would live with a Yellow Watchman Goby and a mated pair of Clowns.

I've always wondered what manufactures really mean when they give dosing instructions based on "gallons." For example, Korallen-Zucht and Red Sea give dosing instructions for their additives in terms of X ml or X drops per 25 gallons. Gallons of what? Is it based on the rated tank size (my...