I want to make pasta at some point and I am wondering if I could use all whole wheat flour instead of a blend of all-purpose and semolina flour. I know the taste will be a little different, but can I use only whole wheat flour instead of AP and semolina for pasta?
You can, although the vast majority of whole wheat pasta recipes also include flours that are not whole wheat. When I first answered this question I missed that you were looking to make pasta using only whole wheat flour.
One way it can work to use all whole wheat is to make the dough, knead, and then rest it overnight recipe, but I'm a bit dubious that the final result will be completely satisfactory. Simply put, if using whole wheat alone can make good pasta, we would see more recipes that only include whole wheat.
If you search for "whole wheat pasta recipe" you will find many recipes that include whole wheat and another flour. The ratio of whole wheat to other flours will vary, I'd definitely look for recipes from very solid sources or recipes that have many excellent reviews. There are a lot of not-very-good recipes out there.
Of all the recipes I looked at from sources that I trust, Mario Batali's uses the highest proportion of whole wheat. He uses a 7:1 ratio. The reviews on that particular recipe aren't stellar, but the comments suggest that the reviewers liked the pasta, just not the sauce.
Yes you can use only whole wheat flour and no, you don't need to rest it. I would suggest whole grain pastry flour since it is ground finer than standard flour and will be less grainy (I use Bobs Red Mill Organic Whole Wheat Pastry Flour)
Regarding resting the dough, many chefs swear this is absolutely required, others don't bother. I recently conducted a very unscientific experiment with my own family where I prepared the exact same recipe using the flour I mention above. I rested one batch for 30 minutes and cooked it with a fresh, unrested batch. The results were unanimous and my family chose the unrested pasta.
100% whole wheat works fine. The reason you don't see such recipes online is that so few people cook this way.
Resting is more important if you are making pasta without a machine. When using a machine, put the dough through on the largest setting, fold it over and do it again and again. At one point you will get to the smooth texture that you are looking for.