Ranking NoComp KW's with web2.0s?

I want to rank kw's with literally NoCompetition the #1 is an semi authority forum post with 0 backlinks and 5 words of content.
Is it a good idea to make a web2.0 for this kw ? I plan to make a wordpress.com blog with one article with around 500-700 words of content and give it 200-500 social signals.

Do I need backlinks to rank?
Does anyone succeeded in ranking extremely low comp keywords just with a small gsa blast of maybe 1-3k backlinks?

As long as the keyword has search volume, you will need backlinks to rank for it, even if it is just a few. Be careful when building links to wordpress.com blogs. They are known to delete blogs blasted with spammy backlinks from tools like GSA.

I recommend you avoid wordpress. They are a bit aggressive with their banning. Maybe try Yola or Weebly.