The Pro Trinket Lion/Lipoly Backpack will be soldered on to the Pro Trinket using the included headers.
Add the on/off switch to the switch pads on the Backpack, remembering to cut the trace between the two pads to enable the switch.
The button will be wired to pin 4 and G, and the LED sequin will be wired to pin 5 and G -- it's convenient to use the other leg of the button since G pins are a bit in short supply.
Connect the neopixel strip data to pin 3 (remember to connect from the "in" end) and connect the 5v and G pins to the + and - pads on the back of the Pro Trinket.
Plug the battery into the charger and you'll be good to go! You'll be able to charge the battery without opening the case via the USB port on the Pro Trinket.