Router would be the way to go, if the static address is assigned from a device by itself which is not always online, there is always a chance of router assigning that IP to another device.
One more thing - when I reflash a new version, or use a different card, will that change the mac address? Or ‘this physical pi’ will always have that mac?
The MAC address is hardcoded into the network card on your pi, it will never change. You have 2 options here, set a static ip outside the dynamic range that your router uses, or leave the pi on dynamic and set your router to always assign the same ip to it.
More or less as you would like … taking on board that routers usually offer a single contiguous range for DHCP leases. By convention only, 192.168.x.1 would normally be assigned to the router/gateway.
You’ve found your solution, but for others I thought I’d add something about IP reservations. Many talk about the “router” reserving the IP. Strictly speaking, it’s the DHCP server that does - it’s just that most modern routers have a DHCP server built in. The DHCP service is what allocates the IP address, and to ensure that your devices get the same IP’s every time, you can do what they call a reserved IP. That means that whatever IP the DHCP service allocated, it will continue to do so in perpetuity even if your device goes off line for a while.
-Hugh