you need to try and establish how much competition there is for the keyword - not adwords competition, but what your actual competitors sites are like.
there are lots of tools out there that will do this.
Also, as IamBlackhatter said, dont just try and build your site specifically for that term, have a goal of making it an authority site.
My advice would be to build a big list of keywords before you start - keep your main keyword, but also have a content plan and create articles regularly based on your big (longtail) keyword list.
that way, you will find that you'll probably start ranking a lot of sub pages before you rank your main keyword, and you will get some traffic and revenue from these in the short term.
But also, they will give your site much more credibility and help you to rank for your main keyword.