Domain Name

Ok, I'm thinking about makeing a central server for my home network that will serve anywhere from 1 to 3 purposes. At the very least, it will be a place for all the networked computers (1 linux laptop, 2 xp desktops, mabey 1 win xp laptop) can store shared files. All but one are connected wirelessly right now, there is just no spot for them to share files. I have a cable line going into a cable modem, which goes into a wireless router with 4 ports for wired connections. I will add in another computer that will be the server for all the rest to store files on. Should i connect the server wired or wirelessly?

The other part that confused me was domain names. I have to pay for a domain name so i can have a website like www.tremallo.com right? I might want it to also hold a website for me, as well as be an email server for my family so everyone will have a @tremallo.com address. Is this possible?? How much would it cost? and should the server run linux or windows? I have some legal copies of windows so money isn't a problem, I just think it would be harder for it to be linux because that would force me to have the server be wired. I know that these are alot of questions, but I can't find any solid anseres on the internet.

-Thanks :D