It's all personal preference really, some use two inch coverage some go by less. I use very little about 1-1/2 inch coverage for my 90gal. some people do not use any at all. if your going to use plants you might want a little more.
If you're not going to use real plants, a very thin layer of sand (1/2"-3/4") really takes a load off of you maintenance wise. However if you're looking at a planted tank, at least 1 1/2" of gravel will do, most plants wouldn't need more than 2".
yeah, just missed the hex part, works pretty good on long tanks for about 1 1/2 to 1 3/4" of gravel, lil less on the talls and hex's and more on the wides