Domains: Domains today are cheap when I started out domains where $100 per year. I use
1and1 they are only $6.99 per year. I have heard some bad things about there hosting, so I wouldn't go that route, but as domain names, they have never done me wrong and I have around 300 domains with them and have been with them for about 5 years at the time of this writting.
To pick your domain try to keep it short, and try to keep it simple. If a surfer can remember your domain name thats half the battle. Don't use terms that a non adult would think would be a site for a non adult. Watch your trademarks. A domain name that is named after a product is a complete no no. Terms like for dummies or r-us will get you in a bind, they are part of a trademarked name.
Try to stay with a .com the reason is .com is the top of the crop for domains. Everyone knows of a .com. Not many know of a .ws or .biz.
When working with search engines here is a little trick I have used over the years. Add the, e, i, or you can use numbers like 1 thru 9. I have found some really short domains 4 letters by useing numbers. No your not going to find 8porn.com but 99pornagraphic has a better shot.
Dashes this has been debated over the years, to dash or no dash that is the question, for search engine the dash doesn't seem to matter, to a surfer it can. If your trying to build traffic as long as its short and easy to remember your pretty much ok..
Footnote: If your in this biz any for any time at all your going to find you buy domains and they sit, blank or empty. I have taken the time to make an index page that you can throw up on your server as an index page. So that it not blank and not making you money. Once you change my affiliate code to yours you can use the page over and over.
You can find it here.