https://islandconstructionnh.com/
Ben and crew did major rebuild for us last year. Roughly 150 linear feet of dock, u-shape. This involved removing 60 year old pre-stressed concrete docks, driving pilings, adding new decks, adding new power pedestals and extending electricity. Excellent work throughout.
DES is usually pretty quick with permits, but they send them to the local Conservation Commission before the application is considered complete. The CC's usually meet monthly and often push the application back if their agenda is already full for this month and/or next. They may add restrictions, so it may be worthwhile for you and your contractor to attend the meetings.