Ducks ARE good at slugs for sure. But you don’t want them to eat TOO many - slugs are full of parasites
You asked a lot of questions. I’ll give it a go at a few. -
Some breeds (khaki campbell) can lay 300+ eggs per year how true?- 100% true
They/certain breeds/species don't require much water, how true and to what extent?
This I never heard of. Ducks need at least a bucket of water, deep enough to dunk their head in and keep their eyes and nares clean. They do not absolutely need a pool to swim in however it is recommended to keep them themselves clean and they have so much fun swimming in a pool, I fill their pools whenever the weather allows
How messy are they?- haha they are messy with water. Yes they like to make mud so put your pools or buckets in a place where the downflow goes out of your yard not into it. And don’t give them water inside of their coop unless it’s extremely hot in there I do it occasionally in the middle of summer when we get days that feel like 112, the coupe only cools down to about 80-90 at night, so I give them a water bucket, but it’s a lot of wet bedding the next morning.
How much space do they need?
They need a minimum of 4 ft.² each for their coop, sleeping quarters. As far as Outside my 18 ducks presently have 2000 ft.² or so, if you are going to keep them in a run, I don’t really remember what the standard requirement is, but I wouldn’t want them to have less than 100 ft.² each if they had to be in a run and not get to free range on a regular basis.
What kind of shelter do they need? Very secure and sturdy building four square feet each and must have one square foot each of ventilation up high above their heads at the top of the walls , all windows covered securely with half inch hardware cloth (I use two layers one inside and one out) a gentle slope ramp is OK for them. It must be wider than for chickens. Their house should be off the ground, but not too high. It needs ventilation underneath, and you should skirt it with hardware cloth around the bottom. I dug into the ground 2 feet deep sort of a moat around my duck house and put the hardware cloth going down into it and then bent it going out 2 feet. Then filled it in with dirt. Anything that tries to dig will not get under.
How hardy are they compared to chickens?
In my opinion, ducks are hardier than chickens. They don’t get parasites or worms nearly as much as chickens. I’ve never had a parasite or worm issue for 12 years with Ducks, but I had chickens for three years and had all kinds of issues with that stuff . Had to buy dewormers and parasite sprays and powders., etc also had crop issues with chickens never had one with a duck. And the chickens need shelter from rain during the day, but the ducks have a party when it rains.
How quiet are they? That depends. I have a few that are quiet, but some are pretty loud my Pekin and silver Apple yard are my loudest right now. I also have a golden 300 That’s pretty loud.
How needy? / what do you mean by needy? Ducks need to be with other Ducks but they don’t need your presence however you will enjoy it if you hang out with them of course they need clean water every day. They need to be fed proper feed and have secure housing most especially overnight.
What breeds are best?- This is certainly a matter of opinion.
I believe golden 300s are one of the best at being hardy and laying eggs, runners are the best at entertaining you, Welsh Harley Quinn’s are the best eye candy, pekins are the best at waddling, lol oh and Cayugas are also gorgeous and mine has been pretty quiet. Khaki Campbell’s also quite hardy and tends to be quieter than others., and They do lay a lot of eggs. They can fly a little more than some of my other breeds so I had to make my fences a tad taller.
I'd love for them to be able to free range so I think clipping wings would have to be done if we got any of the more flighty breeds. I've never done that before though and don't know how recommended or not it is.
