Congrats on your new Argosy and welcome to the forums. Sounds like you found the perfect Airstream for you. The fact that it has a good skin is a real plus. Repairs to the interior and making improvements, you can do at your own pace as time and funds allow. Functionally there is really no difference between a new 70k Airstream and the 2k model you found, especially after you get finished making it your own. Your kids are really lucky; sounds like they know it too.
Last time my wife and I went to Maine was over 30 years ago on a BMW motorcycle. Wonderful trip. Time to return to Maine in the Airstream.