No worries. Zigbee is the same worldwide but Z-Wave is not. I have a vendor I like but they are just for North America. Aeotec seems to be popular vendor. I would avoid the cheap Chinese Neo Coolcam stuff though. From experience, they do not necessarily work well.
Some battery operated devices have an option to power off USB if that is desirable.
Zigbee & Z-Wave are designed to handle low power battery operates Smart Home devices. Wi-Fi is battery hungry and has a lot of network overhead.