Any SEO expert gives me a replay?

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There are two questions here, plz give me some right info.
1 http://cosplaycostumes.blog.com/ This is my blog, I am wondering if I should separate the domain name into cosplay-costumes, there is a saying that Google will say the two words with a word, it is bad for my site. But, someone says that it is no need for the use of "-". So, could you tell me what is Google's really idea?
2 I am wondering where to add description to my this blog I mentioned above, from the blog.com.
And could you please tell me the lastest rule of Description, in order to make the site have a better ranking.

I am a seo rookie, any help will be thankful.