IMHO, boating in the San Juans and the Gulf islands is much more challenging than further north because of the swarms of boaters, ferries and complex currents. The actual passage to Alaska is quite easy. Only two open water passages and they are easy if you listen to the weather forecast. Remember, people make this trip in kayaks, rowboats and even engineless sailboats.
Navigation is easy because of electronic charting, radar and AIS. Other than these items keep the boat as simple as possible to avoid breakdowns. Knowing how to maintain and service the onboard infrastructure is VERY important. North of Pt. Hardy and South of Ketchikan you are on your own.
The first time I made this trip (Seattle to Glacier Bay in 1992) I only had inland experience and had no problems whatsoever. This was before all the modern electronics.
Douglas book is sufficient to get you up and back with few problems. Just do it before life gets in the way.