No it is not require to have many blogs to win the contest. Contest is all about getting members from your blog to gaf forum. An I had added two of my blogs and I managed to get traffic to this forum using mu earning blog.

You have to add RSS feed to the blog thats it. You can try this one but I think this month admin has Paused this contest. I wish he will add some more contests again.
I don't know either about RSS feed or about the blog contest, but it seems Bigmum monthly selects the winners by random.org. Right now the site is down and it seems again it's under DDOS attack. Let's hope it will come back soon.