Greetings,
I have an online BDSM Gear/Adult toy/lingerie/fetish store, and have come up against many problems regarding finding a host, a credit card processor and a host of other issues.
My first concern would be to consult an attorney regarding the legalities of the kind of site you are looking at building, especially regarding the 18 USC 2257: law, in which you have to have the models sign a release confirming their age(over 18) and keep records proving such with their names, addresses and other details in case of problems with the "authorities" and that you have the copyright over their pictures. There is a website that covers a lot of the legalities at http://www.adultinternetlaw.com/ Have a look at their "Articles" "Content" and "Newbie" sections
Paypal, is definitely a no-no for any adult related site, once they find out (and you can bet they will) they will shut you down so fast you wont see the dust, or any money that is in your account for whatever reason.
CCBill and IBill have been up and down regarding what is and is not acceptable and have heard a few horror stories, but I have never used them. Many problems regarding VISA credit cards have cropped up lately too with them charging exorbitant amounts of money for adult orientated sites.
ONe of the best resources I have found for any questions I had, to be the YNOT website (http://www.ynot.com/) They have a good message board with lots of advice for newbies, covering everything you could think of. Also they have links to a lot of adult orientated hosting companies, Age verification companies, CC processors etc.. They also keep up with what is happening out there in the adult entertainment world regarding laws etc.
Whatever happens, cover your a$$ legally, expect to spend a lot of money setting it up and waiting time for it to get known and hit on. Advertising is another kettle of fish, again YNOT will give you clues on how to get the most out of your advertising dollar.
Web design is obviously another aspect you have to look at, if you have the time, energy and knowledge it can be very rewarding to put up your own site, on the other hand it can be a complete pain (and not the good kind) in the rear end to update and upkeep. If you have the money, hire a web design company to take care of it
Good Luck with your site.
Best Wishes
Lucy