So far and from my understanding no minimal and maximal post required to earn merits and if you post something that is helpful to community you would see merits coming like flood to your profile,as a matter of fact a single post can possibly earn you up to 100 merits depending on creativity and useful you information could be. The thing is most of the topic created by newbie are the topics already created but just that they always reform it make it looks like another post or I will say there is always a particular methods mostly used by some newbie to earn merits and since lots of people knows giving out merits to similar post could be very hard.
Yes, I've seen one newbie get merited on his first post, and there are newbies with thousands of posts who haven't got a single merit because all these newbie posts are about bounty submission reports, which do not offer something useful to the community but to the project they promote.
So newbies who are active in discussion are likely to get merit then those who participated in bounty campaign.
So, if you concentrate on the discussion, continue doing so. There are threads where you can submit your best post to be merited.
But newbies who participate in various discussions can definitely earn merit.