oh...to answer questions 2 and 3:
for the question about HOW to set it up. I'd read a HOWTO or if you have a few extra dollars, get the book DNS and BIND (an O'Rielly book).
i registered my domain at a website www.urlcollection.com
they were the cheapest i could find 12bucks a year.
there are like hundreds of sites that let you register domain names. this is not a commericial for urlcollection but..with them i use their nameservers and add all the CNAME, A, MX, MXE and URL records i want.
if you have a dynamic ip address though, it makes things a lot more complicated and you might have to pay to have a company keep up with your ip address as it changes (like dynu.com, if you have a REAL domain name and want to use their nameservers for a dynamic IP, they charge u like 35 dollars a year and you have to run software that notifies them when you IP changes so that they may update the A records for you domain).
if you want to get a really clear picture of how it all works, i suggest either getting that book or reading a decent howto that explains it all in greater detail.