1 post is enough if it deserves for merits. But that post must have good quality and useful for others. However, merits can be quite subjective, each member may view your post in a different perception. Even if you assume you have made quality posts, other may assume the posts as average posts. I think you just need to make harder efforts and analyze how other posts can get merits.

There should be a minimal. If you have no post, how people can give you merits? 
But it is true that we have no maximum posts to be merited.