1. Residence is not free, it much more expensive that regular residence (I think it was QR5000 per person per year).
  2. The residence law has not been applied yet, they may set more conditions other than a 99-year "purchase" (could include nationality, age, education, ...etc.).
  3. You cannot work with that type of residence. You can stay in the country.
  4. You could still be thrown out of the country, it's not a "get out of jail free" card.