If you reduce the brightness of the matrix, powering everything via USB should be sufficient for testing.
However, it is recommended to use a high-quality power supply for normal operation. A 20W (5V/4A) power supply is sufficient for this.
TIP
The 1000uF capacitor prevents the initial onrush of current from damaging the pixels. It also provides a small power reservoir for abrupt changes in brightness that the power source might not otherwise handle. Otherwise it can happen that the microcontroller restarts or it comes to gliches in the matrix.
The touch sensors have two solder bridges on the board which can be connected. This allows switching between active high (when pressing high) and active low (when pressing low). This is absolutely necessary for the middle sensor (Btn 2), otherwise the wemos will not start. To prevent this, bridge A of the middle touch sensor must be closed. This sets the I/O pin to active low. Other touch sensors are not recommended, because they have no possibility to be set to active low.