It's the best bet they had. Most of Akatsuki is dead, and if they want to start a war, they have to keep everyone organised anyway.
Pain's nuke was a really rare technique. I doubt there are many nuking ninjutsu left in this world. And you're right in that they did mention they'd create a nuke out of all the collected beasts. They're still missing two of them though.
I think you needed just the DNA of the person. That's why Madara fought the 1st.The whole Edo Tensei thing also bothers me - Do you need the bodies? Can you resurrect people consumed by Death? etc. - but I guess I'll just have to be patient and wait for episode 264.