Ducks are pretty social animals. I'd suggest you get 2.
Disclaimer: I am in no way responsible for what happens after your first 2 ducks.
Disclosure: I started with 2 last August. Now I have 11 including 3 hatchlings.
husha no one warned me of the addiciton and I REFUSE to warn anyone else...I have 11 thinking I would keep just a trio of each breed (6 total) and now I am looking for another coop to house the at least three bachelor drakes I will have extra because I am keeping them all dang it.