As long as you're linking to quality sites, those links will not directly hurt your rankings. If they are good for users and don't make your site look too spammy, then use them.
The general best practice is to have no more than 100 links on a page (followed or nofollowed). The main reason for this is that each link detracts from the amount of PageRank that flows through the links. This is meaningful for controlling the internal linking structure of your site to maximize your site's PageRank and help Google to understand which pages are most important. You can get an idea of how the PageRank link juice flows using this tool: http://www.ecreativeim.com/pagerank-link-juice-calculator.php
But if you really need to have more than 100 links, then use more than 100. Ultimately what gives the best experience for your users is going to help your site the most -- and while PageRank is still a ranking factor, it's not a top one.