Right in no particular order.
One.com's terms state
Illegal material is not permitted on any of One.com's servers, whether this be images, film cuts or hyperlink images or
suchlike material. Nor is it permitted to store erotic, pornographic or other offensive material on servers owned by
One.com. It is entirely One.com's decision to determine whether material belongs to one or more of the above
categories, and the company reserves the right to delete any such material at any time without notice. In the event of
such material being deleted the customer cannot advance any claim against One.com related to the deletion.
So I would be wary about using them for an escort site.
The same applies to any "free" hosting, most will not allow adult content.
XXX domains, personally I think they are a gimmick and would stick with .co.uk or .com
Many hosts will allow you to point more than one domain at a site, if they don't you can often forward the domain from where you register it.
You can usually register a domain somewhere else and have it point at where you host your site.
.co.uk domains have no privacy protection. at your risk you could register it in your working name and use a duff address, some ladies do that ok, you could find somebody who will let you use their details on your behalf, I know xw5's yourescortsite offers that but not sure if its just for people who buy their package, no doubt he will be here soon and can clarify that.
You can have .com privacy, godaddy and 123-reg who I use both offer that with no fuss costs about a fiver on top of the domain.