Hey,
Everything you suggested sounds fine.
Young ducklings (until about 2/3 weeks old) can be fed on starter foods such as Chickcrumb. But this is very rich in protein and thickens the blood, so don't feed this to the ducklings when the start developing their feathers, as the newly developing feathers will be to heavy for the wing muscles and could cause problems such as Slipped Wing AKA Angel Wing, and also Dropped Wing.
Once they reach that age they can eat mixed corns and grains. Also ducks love lettuce, grass, and small amounts of bread (as it sweels in their digestive tract).
If you get young ducklings, there are a few things to remember.
Always keep them warm and dry, many ducklings die within the first 2 weeks due to developing a chill. They shouldn't be allowed to swim for the first week, and even after then they should only be allowed for a swim for about 5-15 mins every couple of days. As they won't have their mother to keep them warm and dry, and they won't aquire any of her natural waterproof oils (ducklings until the age of about 2 weeks aren't waterproof).
As for their enclosure/pen,chicken wire is good, although make sure the ducklings can't escape between the holes, or even get caught and stuck. When they get older they shouldn't try to escape but if they do, just clip their wings.
Locking them up at night is a very good idea, its helps to settle them into roosting and protects them from predators. Straw or hay is a good bedding material as it keeps them warm and dry.
While the ducklings are young it'll help if you can provide them with a heat lamp to keep them warm.
For their exercise pen, try to give them as much space as possible, them more the better really.
And a childs pool may be ok, if they can both get in and out with no problems.
If you gt any more questions, don't hesitate to ask.
Mel X 
