Helllo and welcome to the forums!

Question 3) I'm not sure, but I think so.
Question 4) Leopard will ship with any new computer that you buy from Apple right now. That's why you're eligible for the $30 upgrade price. If you were on Tiger I think it costs more.
Question 5) Well, there are some basic differences between Windows Machines and Macs. I won't talk about that here, but I'll try and find you some FAQ's or Stickies from somewhere.