Assuming you're talking about Meraki devices and their management network, much of it personal preference.
I typically use DHCP as I'm not too concerned about the exact address they pick up and I can always check it's leased address on the dashboard.
For DNS I typically use a public DNS (Google or CloudFlare). I don't use Meraki NAT for any WiFi offerings, but if I did, I'd consider changing the DNS to a service that offers some additional protections.
Apart from L3 gateways, I never use static IP addresses for Meraki device management. Switches, APs, cameras, everything.
Pure dynamic. No reservations.
I do use reservations for things like printers.
>Use Google DNS for each device?
Sometimes I use internal DNS, sometimes I use public DNS. I often use 22.214.171.124 and 126.96.36.199, as I have had customers whose ISP lost connectivity to Google DNS, and it is a bit catastrophic, so I like using two different DNS providers.