Ok, soon I'll be purchasing a domain name to go with a host, and I'd just like a few questions cleared up.

What's the difference between one domain name company and another? One site offers $35 for one year, and another offers $15. Does where I buy mine from affect anything?

I was under the impression that it's up to the host whether or not you have pop-up adverts. Am I right in thinking the domain has nothing to do with this?

If the last question in the first paragraph is yes, anyone recommend a good one? I'm not too bothered about an email address, but my host says I'll get one anyway. Or something.

Thanks.