It's about quality not quantity. You could make 1,500 posts that are utter garbage, yet that's pretty much the equivalent of somebody who makes 300 really good posts that add significant value.
From my perspective as a former natmod, the main thing you need to have is a willingness to contribute in a positive way. That may mean writing guides, answering questions, keeping your section tidy etc.. It doesn't mean being active 24/7 but it does mean that you should come on every so often and help out, especially in the section you've been assigned. Probably the thing that frustrated me the most when new mods were appointed were the ones that just wanted the title and did (PG rated) not so much after they were given it.
Imagine if posts in spam sections e.g. forum games were counted, i'm sure majority of users would have significantly inflated post counts. Do all those posts count as quality? Hardly. Point is, you can still have a massive impact even if you post waaay less than somebody else.
If you think you're somebody who can improve the positive environment (whatever your post count is), then hey, just go for it and see what happens! You can't have too many nice people wanting to contribute to the growth of a student community!