I'm more of a lurker, I only post on a post here and there from time to time, and I got M+ in 2 weeks (there was a sale). My advise is to not see it as a grind where you have to find something to post everywhere you
can, just look for threads or posts in them that you feel you can
add something of value to. And yes, just your simple opinion on a question
is adding value! Do this and you might suddenly find yourself with enough coins in less time than you thought, and since you have just been (semi-) naturally communicating with us here it won't have felt like a chore at all! That was the important part for me.
And I'm still doing the same thing, just checking the site a few times a day, seeing if there's something of interest. Most days so far I do not have anything I want posting, yet I'm sure I will still get the highest rank in less than 4 months

. I feel no need to try to get it faster, could be 5 months for all I care, I just don't want to force myself to view coins as the goal and posting as a means. It should be the other way around or it won't be healthy.