1. Install and run certbot (+the DNS plugin for your DNS provider).
2. Find an nginx config file on the internet that only includes the necessary ciphers to work on modern devices. Then include that config file + lines to your cert paths that certbot spits out into your nginx config.
3. Set up a generic redirect server block to send everything on port 80 to port 443.
4. Reboot nginx.
It's at least better than fiddling with openssl directly, but this isn't fun, it's busywork.