Hi!
I can answer a couple of questions. I have a little flock of eleven nine-week old runners. They are wonderful.
I recall duck eggs as being fine to eat, not so gamey. I think it would depend on the feed, partly.
Not sure exactly what you are thinking with the tub - you mean for swimming? I don't know about chicks, but you probably need to be cautious with them around water. Ducklings have no oil of their own on their feathers at first, but they do need a little bath - 90 degrees F, a couple of inches deep the first week, then just as warm but up to their bellies as they grow, until their feathers come in and they can float and insulate themselves a bit. After about 6 or 7 weeks, mine could jump into cooler water easily - of course, the "pool" was shallow enough they can easily hop in and out. With little ones, they need to be in water no more than 3 to 5 minutes at first, and then right into a warm, dry brooder. Some need help drying off at first.
If you put a ramp up to the tub, there will need to be a ramp out of the tub (inside the tub), too. Ducklings can drown.
Ducks and chickens in small numbers can generally get along. It depends on the individuals. Same with eating eggs, I would guess.
Do not worm ducks unless you are sure they need it. They do not tend to get as many diseases and parasites as chickens from what I hear. But living with chickens they may pick up more things than ducks on their own. Let's hope someone who keeps both can weigh in.
If you raise the ducklings with lots of sweet attention and a few healthy treats, they will likely hang around fairly close, but since free range can mean a few different things (depending on the size and layout of your place), I won't say they won't roam.
I used waterfowl starter and now feed Nutrena grower/maintenance, with some greens and sometimes a few peas. Mine also like slugs.
What is flock block?
Hope this helps.