Hiya, growers are fine for now, they will need to go onto maintenance at about 12 weeks, then layers pellets when they start laying.
Here is a good resource for duck information:
http://pets.groups.yahoo.com/group/petducksrus/files/
you may need to join the group to access the files though.
Lettuce is fine but the thing you need to be aware of is this: Iceberg lettuce has no nutritional value to your duck, as such if you feed too much of it, they will fill up on this and not eat their required ration of pellets. Keep treat to the afternoon so they eat the good stuff during the day.
Good treats are tomato, cucumber, corguette any kind of salad. Dont feed them mushrooms, avacado onions or potato and chop their treats up small. It is good to find out what their fav is as you can bribe them with this if you ever need to handle them or take them to the vet or administer medication.
Careful of mealworms, especially in laying season as too much protein can cause issues.
Bread is a no no for ducks as it contains yeast, ducks can get serious disease from micotoxins (mould) and this includes yeast, hence why ducks in parks dont live very long. Pasta in small amounts is ok too.
zo