Jeff,
It all really depends on how deeply you want to get into all this.
Different areas of the hare's mask will have slightly different characteristics. The guard hairs on the ear portion should be a bit longer and there should be more of them, things like that.
I played with harvesting dubbing from these creepy little bunny faces for a while....as far as the resulting fly was concerend, I could not see appreciable differences between the different locations the fur was harvested from on the mask.
There are as many different colors of hares masks as there have been hares. And, we have also chosen to die them into several dozens of colors too. If you really want to acquire a wide selection of natural colors, you can buy lots of them. In my experience, the fish aren't that picky about color. Especially when you are just talking about a slightly different shade.
I've always found that natrual furs that are suitable for dubbing dub easier than synthetics. You should get lots of flies from one mask, but that depends on the size of your flies and the efficiency of your technique. Cutting the fur off the mask and preparing it for use require some practice and skill.
All of the previous being written, though, I've given up on cutting fur from the bunny faces myself. First, they seriously creep me out. Second, you can buy packaged blended hares ear dubbing (I'm pretty sure that it is made from fur from the whole mask but it could be just ear fur). This stuff has the proper amount of guard hairs in it, dubs easily, will tie hundeds of flies, and comes in a wide range of consistent colors. All the work is already done. It's not expensive. Every fly shop handles it. I'm lazy, and since a bag of ready to go dubbing costs about the same as, or even a bit less than, a hare's mask, it's a no brainer for me.
You'll have to decide for yourself if it matters to the finished fly, or to the fish, if you make your own dubbing or buy it ready to go.
Good Luck!
Buddy
It Just Doesn't Matter....