As far as "search-engine-spider-stoppers" does this also go for "%" in on-page copy?

When an AdWords support rep says something that contradicts the AdWords Help documentation, it's hard to know what to believe. I usually point the contradiction out to the AdWords rep, and they will sometimes do more research to verify for me.

This sounds like expanded broad match to me: http://www.wordstream.com/expanded-broad-match

AFAIK, there is no way to "sneakily" no-follow a link. You no-follow a link by adding rel=nofollow. If rel=nofollow isn't there, the link is followed.

Yes, a new website should claim its brand name on social media immediately, whether or not that improves its rankings. If you don't get your @companyname, someone else will.

You might not get the New York Times to link to an escort site, but that doesn't mean you can't get valuable inbound links. You have two huge advantages: excitement and controversy. The business is about sex. That means you have tons of content creation opportunities. People are interested in sex, talk about sex, write about sex, share content about sex, etc. Same for prostitution. It's a hot political and cultural issue. Sex work clients aren't likely to disclose their pastime on Facebook, but other people might be amused and titillated by stuff on these subjects.

Does your client network with sex workers and sex work advocates online? There are tons of sex-positive bloggers out there. If your client creates compelling, valuable content about sex work, those people might link to it, comment on it, respond to it, etc. Alt weeklies sometimes have columns on these subjects, like the ones by Mistress Matisse and Dan Savage. A lot of these folks are active on Twitter.

Depending on how much risk your client is comfortable with, they could also use HARO and offer expert perspective on the escort biz.

We do what Gerd describes in his comment -- a short description at the top of the page, then the products in the middle of the page, and then additional description at the bottom of the page. Total word count ~500.

Meta-Keywords and Meta-Description no longer contribute to ranking, I thought -- and optimizing Meta-Description is less and less important as Google becomes more likely to use whatever the heck they want for the snippet.

160 well written words are certainly enough for Google to understand what the page is about. Adding more words could help bring in more long-tail, as you include variations on the keyword, modifiers, etc. But you don't want so many words that conversion suffers.

I find that for most keyword phrases, more than twice in ~150 words feels stuffed and unnatural.

Do you have the resources to create unique content for all those pages? Because adding 500,000 pages of duplicate content will absolutely damage your site.