A full set would be 20 12" circles, 9 10" circles and 11 18"x24" rectangles. This is only if you want to set up all 8 stages at the same time.
You would also need 40 target stands.
A simple way, is to build a bracket on the back of the plate and slip it over a 2x4. You will have to replace 2x4's sometimes but it's a cheap and easy way to start. You just cut the 2x4's to the length you need and set them in a wood base.
The stands Wild Rose has were built with steel and are adjustable, which is really nice, especially if the ground is uneven. Also, if you add a spring on the back of the plate, it helps it ring. Nothing is worse than going back to a dead plate because you think you missed.
You should have several spares of each size as well because no matter how you weld them, the brackets on the back will break from time to time. This can be reduced by not shooting full power loads.