Lets start with #3. This comes down to what we are training for. Ifs its hunting, then having a kill zone size target is appropriate. If its competition shooting then having 1 to 2 MOA targets work well. If you are new to long range shooing having 2-3 MOA targets might be needed to get you started and have fun, happy impacts.
Now #1. If the targets is large, like 12" sq inside 400 yards, its not going to do you much good. Inside 400 I like to use the KYLs to push me to hit smaller targets. Having a KYL can help us learn our limits. Limits in our rifle, limits in us, limits in positional shooting, so yes, I find them beneficial. But a KYL can also create bad habits. If we can't quite hit the 4th plate we'll go back to hitting the 3rd plate and not force ourselves to hit that 4th plate. This is where a single plate can help.
Finally #2. You will want targets at further distances to aid in learning wind calling. If we can hit a 3" plate at 300 yards great, but that didn't help you hit a 20"plate at 700 because we haven't learned to call the wind. Having 2 plates are further distances can help a lot. An easy big target to know we are in the right ball park and then a smaller target to really dial in.
When I started putting steel up I started with nice big plates to make easy hits. Then as I got better I moved those plates further away and hung smaller plates in thier place. Finally I added a KYL at 300yds.
Either way, what ever targets you choose, surfing a bullet onto any steel plate the most satisfying immediate response you'll experience. Enjoy.
