I'll add our 2 cents from our experiences.
You want 2 or 3 minimum if possible. They are social birds and need the interaction for proper mental health.
Food/Water... We start with a mason jar chicken waterer and put marbles in the water tray to keep them from drowning. Yes, baby ducks can drown. We make sure they always have food and water also. In our experience, water without food can cause them to get water drunk, which possibly can kill them. We dip their bills in the food and water to teach them to eat/drink. When hand feeding, I add water to the feed (crumbles) to moisten it and make it easier for them to eat and also have water available next to it.
Things may have changed in 10 years, but we stay away from medicated chick starter feed. Ducklings grow VERY fast (I have a Call Duck weight chart and milestones thread here that I posted recently and am updating) and go thru food quickly and they may get too much of the medication. We start with duck/gamebird starter for the first 3 weeks then switch to chick starter.
We put a mostly flat 9" platypus stuffed animal in the brooder when we only had one duckling hatch, and made sure she had LOTS of people time. The heat lamp warms the stuffed animal (not TOO close to the heat lamp for safety) and they cuddle up to it. Keep in mind it's gonna get "messy" pretty quickly and you'll need to wash it every few days after they get older.
We use a large thick black plastic 6" deep cement mixing tub from Lowe's ($16) for their first pool and start at about 1.5-2 weeks old. The black color helps warm the water during the day. Don't let them get too cold. We start with a couple inches of water and supervise them closely, then gradually increase the water depth and swim time as they get older and larger. Bathtub with warm water is another option, but we put down rubberized mesh shelf liner lining because of the slick surface. Slick surfaces are bad for very young ducklings and can cause spraddled legs which they will kill them eventually if not addressed quickly. We use the rubberized shelf lining in the incubator also for this reason. It's cheap and easy to clean.
https://www.walmart.com/ip/EasyLine...-5-ft-Taupe-Shelf-Liner/16451274?athbdg=L1200
If using a kiddie pool when they are older, we use rocks/bricks so they can easily get in/out.
Hens can start quacking as early as 3-4 weeks but some take longer. Males never quack (raspy voice), are larger, and develop a curled feather or two at the base of their tail.
Final notes:
Hens are LOUD as adults. Some are very talkative and some barely talk at all.
They are also very good flyers and can easily fly a couple hundred yards or more. Once they know where "home" is and it's a big enough area where they have/get everything they need/want, you shouldn't have to worry too much about them flying off and not returning, even when they are startled and fly off. Ours have always returned at dusk or earlier after kids startled them. I play loud rock music when I feed/water the animals. They know that means feeding time and gives them a signal to home in on also.
They are a great size for MANY predators including possums, racoons, foxes, coyotes, rats, large snakes, cats, dogs, and ESPECIALLY raptors (hawks in particular). We lose more to hawks than anything. Luckily the crows on the property "usually" keep them away. A secure duck house for at is essential if you keep them outside and a netted covering pen is good if feasible. Without a completely secure coup and pen, you WILL lose some eventually if you keep them outside. You might be surprised how persistent critters can be to get at them, so check your pen/coup often.