1-depends on your patch/lube/ball combo. Some swab after three shots, some after every shot. I hardly ever do unless it gets hard to load.
2-yes patch lube is necessary.
3-nope, cast balls are just fine.
4-I make my own balls and shop around for the best prices on other stuff.
5-Forever and a day.
6-Online in bulk from Powder Inc. or Grafs. etc.
7-Not for a rifled barrel. Harder alloys do not shrink as much when cooling as pure lead does. Therefore they will be bigger and harder to load.
8-Yes, they will last a lifetime if taken care of. I have one that's over 40 years old that still makes good balls.