I am not a contractor (or even qualified to drive a nail in wood) so I will yield to correction by lovinher in case we did anything wrong when we built our room addition with the hot tub. I think we followed most of the guidelines (may have one outlet within 5 ft of the tub), however I will make a couple of other suggestions.
Since we knocked out an existing deck for the room we were above ground level where you entered the room. We made the decision to recess the hot tub into the floor. It really adds to the appearance of the room with a sunken hot tub. The one negative is that even though we planned the area under the room to make servicability easy (e.g. good size entry, extra large cement pad which comes right up to the entry, etc) we are subject to an extra labor charge since they must go under the room.
My wife (much more talented than me) worked with a friend and did an excellent job of doing the interior walls in redwood and staining and sealing them.
Not sure you will get all the steam and condensation during the winter that we do north of you, but we went with an outdoor rated ceiling fan because of the moisture we thought it would be exposed to (and during the winter there is a lot of condensation on it).
One other item that really adds to the room (I love to spend other people's money ), is a fireplace. While my wife wanted a wood burning fireplace, we realized that we would frequently want to get in for a quick dip at night and not want to fool with starting a fire so we went with propane (we do not have natural gas run to the house so that was not a practical option). We were also told that because of the moisture (with chemicals) we should not use a vent free. It's really nice to go out in the evening, turn on the fireplace and relax with a glass of champagne before going to bed.
Tom