I just read this thread from 3 years ago and now I know why so many people complain about raising ducklings due to the mess and smell of wet bedding. I personally would recommend using washable shelf liner in a plastic tub with channels in the bottom to catch water spills and the liquid poop that goes through the liner while the ducklings stay clean and dry. If you only have the ducklings inside for a month I guess anything is tolerable short term but we have ducklings hatching over a six month period so we have had to embrace the fact that ducklings love water and they need a different care set-up than chicks (although we use shelf liner for chicks too and we hatch them year round). We only use shavings outdoors in our chicken coops and never straw because it grows mold and I am deathly allergic to mold.
Ducklings need to have access to water deep enough to clean their bills and they need swim time (yes, they will get wet). I knew someone who had ducklings for the first time and she was hysterical trying to get them out of the rain and into a duck house they wanted nothing to do with so they refused to go inside. She was actually crying when I asked her what was wrong and she sobbed, "The ducks are getting wet!" I was laughing silently as I told her to stop chasing them and just watch. The ducks were wagging their tails and splashing in the puddles like happy ducks do. No matter how much you want them to stay dry they will always want to be ducks and act like ducks. There is a reason they have webbed feet and bills, lol.
We feed Purina Flock Raiser, which is 18% protein and perfect for all stages of growth and adults. It has the niacin and all the vitamins they need so you don't have to fuss with supplements. If you like to make things more complicated you can alter other feeds to make them suitable for ducks but we find it easier to just feed them what what they need right out of the bag (we also feed it to our Orpingtons and Silkies because it is complete for them too).