True. You may comment on your food order what your beverage preference is, and they may stock it in the fridge. For example, ours is champagne. We notified them, and there were a couple of bottles is the fridge. Obviously this would only work for certain drinks.
Overlord Tours is mentioned regularly on the France board, where LeHavre is:
https://boards.cruisecritic.com/forum/462-france-ports/
Great operation...but I seriously doubt they will provide transport to Paris, given the distance involved. For more tour vendor options and transport, look on the France board.
If you read around the board here, you will see the topic discussed frequently. The advantages of the one way is generally, more glacier and port time. The round trip is generally less. However, the 10 day is a pretty unique cruise...you should compare port and glacier times to the 7 day one way routes.
Best to ask on the NCL board, here:
https://boards.cruisecritic.com/forum/64-norwegian-cruise-line/
Can't speak directly to the NCL issue, but, generally, creating an account is NOT the same as downloading the app. We have had a HAL account for years, but didn't download the HAL app until last year, when it became available.
The better place for your research would be the NCL board, here:
https://boards.cruisecritic.com/forum/64-norwegian-cruise-line/
We don't know your budget, interest, limitations, or anything about you....sort of hard to help you.
In all the main Alaska ports, there will be a booth selling tours and related stuff. Supply can easily be limited as the tourism infrastructure in Alaska is definitely limited.
If you get the older terminal with the lounge waiting area, there are a couple of vending machines. I have no idea what's in them. It is after your carry on luggage has been scanned.
You simply do the stuff you would at a US airport to clear Immigration. Customs will vary a little if you are connecting or not, but it's really not an issue to meet Customs. Immigration is potentially the more complicated process.