What power supply should I use?
I am wondering about what voltage my external power will need to be to control all of them at 6v


Well that would be 6V then wouldn't it?

You're asking the wrong question. The question you should be asking is:


  How much current will I need from my 6V power supply?


And the answer is:

Add up the total current required by all of the devices and that is the minimum current the PSU has to provide

On top of that you need to consider how long the supply should last. The average current need to draw from the batteries, multiplied by the number of hours you need it to run for, is the minimum capacity of battery you need.

For instance, if you need to draw an average of 500mA for 6 hours then you need (0.5*6 =) 3Ah (or 3000mAh) batteries (or better).