How much power for my circuit?
What you are describing is one of the fundamental laws of electronics, called series and parallel circuits. There are many references for such topics, however Ibiblio has been hosting Tony Kuphaldt's excellent series, Lessons In Electric Circuits for nearly a decade. The first volume, 1-DC, will explain how this works and why.

The short answer is, you could try wiring each motor to each other motor, then power the entire string of them with 50V. This would be wiring them in "series." In theory this sounds logical, but in reality there are many issues with this method. The motors do not all start at the same time or rate, so one may "see" 3 volts while another "sees" 20 volts (and promptly burns out.) Instead, the better way is to connect each motor's red (+) and black (-) terminals together, otherwise known as parallel, and power all of them from one 5V source. Of course you'll need more "energy" to spin 10 motors all wired together this way, and the chapter about Ohm's Law will make this more clear.