Inexperienced rider - double chainring?
I went to college in Seattle and love the town. Very bicycle friendly town.  It does have ups and downs but the bike paths are pretty flat. If you you live on one of the hills then yes you may have a short steep section.  

As cassettes have gotten bigger (9+) you can get a pretty big range so triple is less common.  Get a compact up front so you can use a 34T for the smaller. The 8 speed cassette bike you are looking at is 32T so you are pretty close to 1:1 which is a strong climber.  With a 9 speed you can get a 34 with the same spacing for a 1:1.  But a 9 speed will be a jump in price.

As an inexperienced rider with stop and go type traffic of a big city a hybrid or city type bike might be a better choice over a pure road bike.