They don't grow as fast as an oscar or Redtail Cat, but 100g should last you enough time to build the pond. Remember that they are sturgeon, so they may look like they fit in the tank fine, but they really need swimming room and lots of oxygen to stay healthy and happy. I have mine in my basement, and don't need a chiller for it. in WA unless its like right in the middle of august or something, you probably wont need it, and quiet frankly even then because it would be a gradual temp change (make sure your ponds deep enough to allow for slow temp changes) it would probably be fine without a chiller.
(before I say that, where in WA are you?)