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.