Quite frankly, I don't want any of those. I never want Futurama and Simpsons to have a tv crossover. It would be hard to stage a Futurama: Toddlers series considering the fact that if they ever were accidently youthinzed(ha bad pun) again, they could just go to the aging planet once more. Plus, after an episode or so, it woludn't be funny anymore. All My Circuits works as small little skits on Futurama, but actually watching 30 minutes of it would be kind of tiresome. I don't even have to go into Morbo reading the news because you were obviously joking there. A musical would have the same problem as All My Circuits, and, finally, Cubert and Dwight annoy me, so I wouldn't want to watch a series with them
However, I do sort of like Doctor Zoidberg and the Zapp's Army ideas. Doctor Zoidberg is my favorite character, but I'm not sure how he would do in show with him as the main character. Also, I don't know where you are going with the Doctor Who thing. I know Doctor Who, but perhaps if you elaborate on it more, I will understand it a bit better. The Zapp's Army one sounds the most appealing, and sense there is no "I don't want a spin off" option, I will pick this. Zapp and Kiff are interesting characters, and then you could have the Futurama crew guest star occasionally, but not so much that it felt like it wasn't a spin off, but Futurama with a new name and more Zapp. However, it could be like a comedic version of Star Trek, and not just have them fighting people, but exploring worlds and stuff.
It's a decent idea, but Futurama seems like a much more ensemble show, which is why it probably couldn't get away with a spin off. However, you have come up with some fairly good ideas, I just think it would be haard ot make them work. Interesting Thread though.