any clue what breed and gender my kids duckling is???
Here's another great post about duckling care.
Yes, it will definitely be much happier with a friend. Please do that! :)
Too young to tell sex at this age (without vent-sexing of course, which should only be done by an experienced person), you'll have to wait until their adult voices start to come in around 6 weeks of age. Females "quack" or honk, males have a quieter, raspy voice. Males will keep their baby voices for much longer than the females. I've had females start sneaking in little honks in between their baby "peeps" as early as a couple weeks old.