what kind of chocolate to use for making candy
It really depends what you're going to do with it exactly, but the rule with chocolate is the same as with other ingredients - use the very best you can buy! It doesn't need to be the darkest dark, or even dark at all (there are some wonderful milk chocolates out there) but it should be very high quality. It will make all the difference. Valrhona makes lovely large chuncks (couverture) of some of their single origin bars that are perfect for making confections at home. I've bought it here before : http://www.chocosphere.com/cgi-bin/webstore/web_store.cgi
Depends on your taste, but I use 70% to 85% cocoa. In most cases price equates to quality - so buy the good stuff.