Some points to ponder: if you are going to be in rural AK such as King Salmon, ATT definitely didn’t work there and from other comments elsewhere, neither did any other carrier other than GCI. It is immensely helpful to have cell access in the event of travel troubles (one person in our party had GCI and it was huge in getting us rebooked and in fact seeing those emails/texts from the WaterTaxi in the first place). You may want to look into a sim/mifi for GCI if you are going to be in poor cell areas. Fwiw, ATT works fine in the towns along the way to Denali and most other places I’ve been to, including Seward etc. (Note there is zero cell service of any kind in Brooks for visitors.)

As for your time frame, early Sept, you should start seeing fall colors, which can be spectacular. From what I remember, Denali around Sept ~21 or so, was slightly past peak but the Kenai on the way to Homer was peak and it was gorgeous. Think that was a couple years ago. For that reason, I love to visit in Sept.

As for the kayak tours or cruises, the cruise operators should have end dates on their calendars since you can book tours in advance. I googled and one operator’s kayak tour to that glacier looks to ends Sept 7. Any others will likely be similar.