That does seem excessive. Change it so that it only sends an update to dyndns when it actually changes.
Having a new ip every 30 hours also seems pretty aggressive. I guess the DNS change might be slow to populate servers in that time if it is a "weird" top level domain.
Dyndns really shouldn't affect your connection, as long as you have a local client that updates your record automatically.
I use jellyfin together with caddy and it was pretty seamless to setup. I configured the caddyfile to redirect my incoming domain to my local ip and the rest worked automatically. It sets up a legitimate certificate for the domain using lets encrypt and automatically renews it.
When you have an encrypted connection, the isp can't see what is being sent between you and the webserver. They can however see your dns-requests unless you have dns over encryption enabled.
The only security measure beyond keeping things up to date that i would recommend is to have a geo-blocker enabled for incoming traffic to your network.
I know someone who did. The police did NOT believe them. But eventually they where convinced to show up at the road close to the lake, as they didn't actually have a code for "hitting wild life with boat".
Sounds like you can't understand your own arguments.