It's really a tough task but with practice anything is possible. I feel like when I sing and play at the same time, I can't do as many complicated fills that I have to focus on. Make sure you know the drum part solid and build the singing melody off of that.
I think drumming and singing would be a lot easier than singing and dancing at the same time. I did it for a talent show type thing and it was pretty hard once you started to sweat and you lost your breath causing you to huff and puff. Also it's pretty hard to synchronize the song you're singing with some of the more complicated dance steps. I should quit smoking as well..
Its not that its all that hard to do it is just when you have to try and play a very complicated rythum and then on top of that try singing or if the drums are much faster than the words coming out of your mouth that can create a timming issue.
But Im sure siging and dancing is hard as well that why you have to work out like the marines. run and sing a cadince as loud as you can.
helps build up your lungs.