Copywriting/Web Content Casino Site

I am looking for someone to write 20 articles a month for a casino website. I would like to test the service out for a month (paid of course) with the option of continuing on a monthly basis if listed below.
Each article should be at least 500 words, all grammatically correct, spellchecked and 100% original content (Copyscape verified ) .Each article will be SEO optimized for one given keyword with 2-4% density.
By agreeing to this job you are also giving us the rights to own the articles and use them on our websites .
Examples of articles needed

Travelling to Las Vegas
Review of 888 online casino
How to play roulette
Betting systems
Review of online slot machines
etc

I would prefer to pay per article, but am open to an hourly rate