BILLs are not mine-able because it's a token  and because it's on the Stellar blockchain which uses the Stellar Consensus Protocol. No mining necessary
  

As far as exchanges go it is way too early to give dates as the public ICO officially starts on September 1st. However there is nothing to stop trading from happening on decentralized exchanges as soon as the ICO tokens are distributed.

If you are interested you can participate in the bounty campaigns or the private sale