The "secret" to not having your crackers come out too hard is to think of them as a type of pie crust and don't over mix or over roll them. Also, you can experiment with different types of shortening. I find that oils tend to make a denser cracker and that solid shortenings makes them flakier. Also keep an eye on the baking times. It's hard at first to make a cracker that's crisp without having it become hardtack! Like anything else, the more you make, the more experienced you will become at knowing how the dough behaves and then you can tweak it.
I made the flax seed cracker recipe by looking at a traidtional cracker recipe and coming up with my own mix of flours that I can have and that tastes good. I'm not gluten intolerant so I use the oat flour in mine. But really, if you kept the same ratio of shortening to flour, you can substitute just about any kind of flour in a cracker recipe.
You can experiement with mixing in such items as parmesian cheese, dried onions, dehydrated veggies, and make all kinds of gourmet crackers.
The funny thing is, if I had not developed wheat allergies, I would never have needed to know how to make my own crackers. It's one of those silver lining things--cuz my family loves home made crackers now AND it's a good thing to know how to do>