This is handled on a case-by-case basis. If you work for a company as their forum rep, we’ll totally do it for you, but we will verify you work for the company (so get them to add you to their website). We also may do it on a whim if someone stands out in a good way, like when Jan was new we jokingly called him the Brute Squad for his handling of spam. The name stuck, just like Ipstenu’s being a half-elf.
To get a custom title, email the wp-forums list and ask nicely.
Linking to your own stuff can be a tricky question. Many of us blog about support issues, and some of us offer services/products to assist with them. It’s a fine line and very easy to cross. In general, if you’re 100% certain that your product can solve the situation at hand, yes, link to it. If ALL of your posts are similar to “Your calendar plugin has a fatal error! Use mine instead!” then you’re actually spamming and we don’t like that at all. If you’re linking to a paid product, be sure to explain that in the post.