What is importance of hops acidity?

I am still very new to brewing, and have only brewed one beer, a Brown Ale w/ Raw Cacao Nibs. I was hoping for a bready brown ale with mild chocolate flavors. What I got was a medium bodied brown ale with earthy spicy notes, very enjoyable but very very mild chocolate flavors. I'm told in the future for more chocolate flavors I might want to use roasted nibs, not raw.

That being said, I'm shooting to try a chocolate porter, but I don't want any bitter hops flavors to come through - I'd love to have either a graham cracker or nutty hops profile with a good chocolate flavor from roasted nibs, if such type of hops exists... I may research fermenting with a touch of honey, cinnamon, and nutmeg in addition, but was looking at this hops chart to help me decide what hops to use for a chocolate beer:

http://www.onebeer.net/hopschart.html

I noticed this chart gives Acidity of hops, and was concerned what importance the acidity of the hops would be when experimenting?

Many thanks!

The alpha acid and the amount of time in the boil determine the bitterness of the resulting beer. To get a less bitter beer you either use a hop that is lower in alpha acid or you add them later in the hour long boil or you simply use less hops. I frequently use Magnum for bittering and since I'm doing a smaller batch, I use half an ounce or maybe even a quarter ounce. Sometimes I might use Cascade hops for bittering because of the lower alpha acid and occasionally I add the hops for 45 minutes instead of the full hour. Lots of ways to control how bitter your beer turns out.

With all that said, beer without bitterness is terribly sweet tasting usually. You need something of a balance between the malty sweetness and the bitterness.

One beer that comes to mind that was disgustingly sweet to me, was Lagunitas Hairy Eyeball. I couldn't finish it alone, as it simply felt like I was sipping on imitation maple syrup. Surprising, coming from Lagunitas.

Many thanks for the info That really helps!