ULA would let you maintain your internal lan with custom subnets and DNS even if you switch carriers or use multiple carriers. No need to update your internal DNS servers for ULA.
If you're running a server on your dynamic residential service, you must be using dyndns for ipv4. So do the same with ipv6.
Residential random prefixes is the nature of residential networks, as ISPs don't want to preserve state. With a business grade service, you'd get a static prefix, much like static ipv4. Then the only time you need to update anything is when you switch your ISP and need to update global DNS addresses for your servers.
[0] Ideally pure v6 if possible; I think there's some way to encapsulate/NAT v4 traffic out from a pure v6 network so I don't actually need dual stack.
Maybe I will write one this weekend and make a hn post.
As for the actual configuration you'll want something specific to your exact network device as learning any of it with a guide for how another device expects the configuration to be entered will be hair pulling.
Multiple carriers has no (consumer level) solution I've found myself happy with. It's anywhere from "hope all your devices handle multiple public prefixes quickly and without errors" to "NAT and deal with the pain you had from v4 again" to "Use some other way to relay or host your static services which need to be externally accessible" to "go back to dealing with trying to automatically update that DNS server entry on and making sure it always stays consistent"