The die will do the seating and crimp in one step if that is how you want to do it.
When I am loading plinking ammo, I do it that way, but I do it in two steps for hunting ammo, for more crimp, and better consistancy.
You can do it in two steps using the same die. To seat, back out the die a few turns, so the crimp doesn't hit the case, and screw in the seating plug so it seats to your desired depth. After seating your bullets, you then back out the seating plug, put a case up into the die, and screw the die down until you feel it hits the case, it then needs to be screwed in another partial turn, how much depends on how much crimp you want.
If you want to do them both in one step, you first start with the die out far enough to not crimp, and seat the bullet to your desired depth, then turn the die in to your desired crimp. With the case fully inserted with the crimp, you then screw in the seating plug until it stops on the top of the bullet.
So another crimp die is not necessary, unless of course you want a different type of crimp on it.
