Since we want these lights as bright as possible, it's best to connect the battery in the middle of the circuit instead of powering from one end. Power flows both ways, but degrades if it has to travel a long way, so hooking up the battery halfway through the strips will give you the most bang for your buck in terms of brightness.
The Circuit Playground Express needs to be connected at the IN end of the strips, since, unlike power, data can only flow one way. So we'll put it at the beginning of the very first strip.
- CPX VOUT --> NeoPixel +5V
- CPX G --> NeoPixel G
- CPX A1 --> NeoPixel IN
Then, we'll connect each of the strips' OUT end to the IN end on the next strip: 5V to 5V, G to G, and OUT to IN.
The on/off switch will be put inline with the red wire (5V) halfway through the run of strips.