One final question to you, how many links do you think is safe to post every day?
I presume you're asking how many links is it safe to place on your own site per day, and to be honest there's no rule for this either, but you should keep the number of links out of any page to a maximum of 50.
If you're asking how many links is it safe to get TO your site, that's a different story. Mainly because you've no control over when a link to your site will be put up - it's in the hands of another webmaster. You could make 100 link requests per day, but it might be weeks before some are active, and days for others.
Instead of focusing on the quantity of links, think more about the quality. One good link from a page with decent PR, few other links out, and content relevant to your own, will do you more good than 50 links from dodgy pages with no PR and no real content. Try to get links from sites that are in the same field of business as your own, but not in direct competition.
A good source of information on linking in particular, and SEO in general, is Jill Whalen's High Rankings. She has answered all these questions, and others you may have later, and her site is easy to search around in. Sign up for her newsletter too, unlike some of the SEO newsletters Jill does not spam you, or pass on your email address.
SEO Consulting: High Rankings Expert Search Engine Optimization: Search Marketing Agency Boston, MA