Can I give myself multiple turns at once with Beacon's of Tomorrows?
You will get it back to back. See Comprehensive Rules.


  500.7. Some effects can give a player extra turns. They do this by adding the turns directly after the specified turn. If a player is
  given multiple extra turns, the extra turns are added one at a time.
  If multiple players are given extra turns, the extra turns are added
  one at a time, in APNAP order (see rule 101.4). The most recently
  created turn will be taken first.