It is good to find a suitable box for the amplifier and the battery. It can be plastic or metal - in the second case an insulation must be put between...
Step 5: Connecting the mute signal.
In the datasheet was seen that the audio amp has a mute pin - your decision : You can have a switch to mute the amplifier, or to connect the pin hard to the supply line for continuous operation.
I connected it directly to supply line.