The shafts you buy from archery suppliers are ready to be made into arrows as is. They are spined into groups, and you can have the nock and point tapers cut if you wish. The dowels are just that, dowels. They will need to be sorted for grain runout, knots, etc. and then flexed to be sure they really want to be arrows. After that, you will need to spine them to your bow. This can be as simple as shooting them to see how they fly, or you can buy or make a spine tester. Remember, a longer arrow and big feathers will cover a lot of variance in spine.
There will be some waste in 100 dowels, but at .25 cents each, it's still worth it, IMO.