I would say, just be sensible and careful with how many links are on your pages. Anywhere between 20 - 70 is fine... above 100 is too many IMO. Links to external sites may "drain" your PR.
It does not matter how many links you provide through making your comments dofollow. Some blog post of Problogger has more than 400 comments. The only factor is that links for affiiliate marketing must be nofollow, otherwise Google will penalize the blog.