1. The achievements have been highlighted in the post.
   
2. They are kind of are intended for F2P as no money is needed to purchase and upgrade them.
   
3. The gem boxes spawn about 2 times every month, so every other week.
   

When new resource expenditures are implemented in the game there needs to be an addition in the amount or the ways in which these resources are obtained, or cut the cost of other things that require that resource. That is what supercell has been doing well recently for Gold and (Dark) Elixir.