Can I stack multiple Hats on my Picar-X (e.g., M.2 Hat)?
In theory, it is possible, but there are some issues. The nylon pillars and 40-pin header included with the Raspberry Pi M.2 Hat are just tall enough to align with the 40-pin socket on the top of the M.2 Hat. Therefore, the length of the header is insufficient to connect other HATs. You need to find a 40-pin header and nylon pillars that are height-compatible.
Considering I have compatible pillars now and 40-pin header compatibility.
The Sunfounder hat supplies the power to Raspberry via the 40-pin. Can it manage this if the m.2 hat in between has another power supply?
The 5V pin on the Sunfounder Robot HAT is unidirectional, and the SOC of the HAT needs to be powered by the power input of the HAT. Therefore, the power from the M.2 HAT will not affect the Robot HAT. However, it is uncertain whether the Robot HAT will impact the M.2 HAT, so it is advisable to consult the technical staff of the M.2 HAT.
Additionally, regarding whether the M.2 HAT can be powered solely by the 5V pin of the Robot HAT, please note that the Robot HAT can provide a total current of 3A, which may not be sufficient.