DNS Best practices

[Zayan5117]

I've recently setup my OPNsense firewall with DNS failover, currently it goes
1. Pi-Hole (Running on a primary server)
2. AdGuard (Running on a separate server)
3. Google DNS
4. Quad9
5. Cloudflare
I'm wondering though if there are any issue that can arise or if there's a best practice as I'm using the "Use System Nameservers" in Unbound DNS instead of unbound itself
Any tips or recommendations would be appreciated