Advice on good hardware
Thinking ahead a bit, many motion sensors have temperature sensors in them (light sensors too), so if you are thinking of adding motion sensors later on, it might be a good idea to get them now. Philips Hue are Zigbee and very good quality (though more expensive than other brands).
USB stick vs gateway
Most people have one or the other for Zigbee - you don’t need both. A Zigbee stick should support devices from all manufacturers, but you need to do your research before you buy - some manufacturers add extra features to devices that go beyond the general spec. A gateway will only support devices from that manufacturer, but it should do so reliably.
A good way forward might be to start with a gateway and move to a USB stick when you are more confident. Again, the Philips Hue bridge is excellent - works pretty much out of the box and has a good integration with HA. If you decide to move to a stick later migrating is pretty straightforward.
There are a lot of good articles on Zigbee in the Home Assistant Cookbook.
Edit: You’re right to go for quality. Beware of cheap Chinese devices.