So I have a main site, pretty big drawing a decent amount from social media. However I was thinking of a few "sub" keywords and researching them, and I have found that those keywords seem to really favor sites with the keyword in the domain. Would it be a good idea to just buy another domain that has the keywords, rank it up via my main site, same content as my main site as well? Maybe buy some authority links from here too? Will the dup content hurt me on the smaller site?