We have Muscovies (genetically nearer a goose) and they won't want to hatch anyone else's eggs except Muscovy, they'll throw them out, they're great mums albeit a bit dosey with their first ever hatch and sometimes produce up to 3 hatches (usually 2) in a season, they don't lay all year, tail off about September until Feb. If you get them at auction you'll get them at a snip as people get inundated with offspring but the lavender ones (grey) go for most money.
Averagely ducks go for about the same as hens at auction.
Call ducks - cute but noisey if you have neighbours and you'd have to hatch in an incubator or a broody hen may do (we have one doing this presently). An all white female may go for around £35 at auction.
Both Calls and Muscovies fly - personally I'm against clipping, flying is a gift and there are plenty other breeds (most in fact) that don't fly, so if you don't want flyers, plenty to choose from. They don't fly away though, just around and about, they know where home is. Eggs, Calls produce a bantam size and Muscovy a big duck egg with a concrete shell and jelly fish in the middle - my OH loves them for poached egg on toast as they stay together in the pan, don't thread out.
Yes you can provide a bath for a splash, a home made pond is a hassle to keep, we're lucky we have a mill pond with a river tailing in one side of it and out the other (a loop off the river if you like) so it has a through flow. If you do a splash around you should change it every couple of weeks but provide a 'dooking bucket' - a normal bucket with water to the brim, so they can get their heads under and throw it back over themselves and drink from it. It should be changed every day.
You will only make pennies from ducks, same as chickens.
We had White Campbells and Runners in the past, they all got taken here by otter - if you have a water course near you tis likely you'll get something using it as a highway which will take non flyers.
Ducks are messy - all that water, watery poo (not like chickens) but they have brilliant social antics that keep you entertained, I'd rather have ducks than hens for lots of reasons.
Do a bit of research but you just need to give it a go - a shed is fine for nights - ours roost in trees and on fences as they fly so we don't house them at night. Don't go to expense initially, they'll fit in whatever but if they don't fly they are a target and you may only get one night in and they're away.
Have a go, it's the best way to learn