I think that if you spend some time, all of your questions will already have answers here on this site. I also rescued a duckling with no knowledge at all. One of the most important things that i have read is making sure ducklings have enough niacin. I went to the health food store and bought a economy size jar of nutritional yeast and sprinkle that on their food.
I personally think that BYC has the best information if your willing to spend the time to find what you need answered.
You can also read Metzer Farms site. They have great information as well.
http://www.metzerfarms.com/BooksAndEquipment.cfm?CustID=2607939&Category=Nutrition
From everything that I have read, the absolute best information is going to come from this book. Maybe you can find it in PDF form so you can have it today. I got it from our local library.
Story's Guide to raising ducks-
http://www.storey.com/book_detail.php?isbn=9781603426923
Here is David's (the author's site)
http://www.holderreadfarm.com/
The meal worms wont be enough for complete nutrition, but it's a start. Make sure that you do not get a medicated starter. I have read from other people's posts that it isnt good for ducklings.
The best food seems (this may be a matter of opinion, this is just what I have read) is the Mazuri brand because it is formulated for PET ducks. Not chickens
http://www.mazuri.com/waterfowl.aspx
Honestly, though I have to tell you that the first two weeks I had my duckling, he ate layer feed and as many meal worms as he could because I didnt know his nutritional needs. He is healthy. I am not telling you to do this, however I am saying that scovies seem to be hearty. Do your research and your ducks will be fine. If you do not plan on keeping these ducks as pets for their entire lives then you DO NEED to give them to someone that has other ducks. These babies need to be taught how to find their own food and survive in the environment.