I run multiple pinholes using keepalived. Then I only use one DNS in my DHCP server. Second pihole will seemlessly take over if the first one goes down whilst using the original DNS address.

Work quite well. I had to learn the hard way that only using a single pihole was just asking for my partner to be mad when it didn’t work / when I was doing server maintenance. Now I have multiple and they can all seemlessly take over if any my server nodes are down

How is your Plex install so big? My library is like 6x larger and my Plex install lives in a 24GB VM