If I understand correct, this will enable me to use separate IP addresses for each container in the same range as my physical units on the network?
I use it for pihole exclusively.
Are there any problems with it that I should know of? Maybe add an internal network so that dockers can talk to each other without going out on the network (it is not a huge problem, the system will be low traffic).
Yes. Your Host/NAS won't be able to talk to it unless you add a MACVLAN to your Host. (This is by design, to increase the seggratation of those containers from the Host itself. I had do that recently, myself. You can do it via the following commands (not reboot persistant)
.2 is my pihole Container with a MACVLAN, .3 is the MACVLAN Interface on the host. Be carefull to not use IPs that are given out by your DHCP.
If you want to make it reboot persistant, add a config file under /etc/network/interfaces.d/interfacename like that: