I live an hour from the Seatac airport here in Washington state and fly exclusively Alaska Airlines(over 20 round trips on Alaska this year) and can provide some insight for you. Alaska Airlines had a horrible spring and early summer which was related to the pandemic and Alaska Airlines not looking to the future for pilot training and a few other issues that were completely Alaska Airlines fault, that said they have resolved those issues and have been pretty reliable for the last half of this year other than unavoidable weather issues.
October is a mild weather for this part of Washington and you shouldn't have to worry about flight cancellations from Alaska or any other airline in October, I wouldn't be afraid to fly Alaska next October. Seatac airport security can be challenging for people who do not have TSA pre-check or Clear so you will need to plan to arrive at the airport 3 hours in advance to check your bags and get through security this will provide you plenty of time to get through everything. I believe Alaska does participate in the bags program if you choose that option. The trip to the airport from the port takes about 20 minutes on a good day during off traffic times but coming off a cruise where 4,000 other passengers are headed to the airport you need to plan in an hour commute, possible more depending on the mode of transportation you choose.
I hope that helps answer some of your questions.