Wouldn't that depend a lot on positioning?Its not necessary as the more you display the more chance you'll start displaying low paying adverts.
true, confirmed by google themselves. So you can use CSS to your advantage to make sure that your most prominent AdSense block is the one that is called first in your HTML code.The first ads in the page code will be the highest paying ads as far as I remember.
Can you not have as many Adsense blocks as Ad slots?
It shouldn't as the Adsense policies only allow for 3 units. So this must be a way to by pass that rule.