24" is the max height I, personally, ever go.
it is the furthest down i can go with my arms to my shoulders without swimming, and it really provides just enough room for real top, mid and bottom lines for the tank and its denizens.
As far as width, i have always been a huge fan of wide tanks over slender ones. Nothing dries me nuts more than a tank that is taller than it is wide - even for discus. It is just an aesthetic that I've never enjoyed, so typically anything 24 inches to 36 is best, if the room it will be in can handle it.
I also do not like too tall of stands.
I have kids, and their favorite activity is to watch the invertebrates wander around the tank, and any stand taller than 30" is way too high for them to enjoy this. Unfortunately, any stand less than this can handle almost no sump or bottom panel maintenance, so it is a tricky situation going that little without extending the footprint of the stand itself in order to account for it.
Sounds to me like you already have what you want in mind.
