The switch accounts work in a way that every account has its own save data for the games, so you could have up to 8 towns with just one copy, even if the game is downloaded digitally.
As for the DLC, every switch is region-free, but Nintendo can still lock DLC to the country of the account, but there is no point in locking DLC, as you can create a second account and get the item, so Nintendo might aswell give it to everybody.
And the switch doesn't have streetpass, or a Nintendo Zone type of software, so the only way DLC can be locked to a region is if you have to get a physical code from a store.