When migrating from Test to Production of a Monero Fork, what needs to be considered? For example, launching the Seed Nodes in "--restricted-rpc" mode.
The only reason you don't have to worry about "--restricted-rpc" in testing is if the test servers are firewalled off from the world so that no external machines can connect.
In production, you need to worry about general operational security and availability/uptime issues. Your nodes should be running on servers that are properly firewalled so that only access to the Monero node ports is possible, and not to other services running on the server.
You'd check you have two factor authentication with your domain host and with your server hosting, so that people don't break into your accounts there and take over your machines. You'd do a standard server hardening, including things such as installing the latest OS updates and only allowing passwordless (public/private key based) access to SSH on the machine.
You'd need to ensure your server had enough bandwidth to serve potentially huge numbers of people that wanted to download from your node, and ensure that you have DDoS mitigation just in case someone wants to take your server down to mess up your big launch.
You'd also want multiple seed nodes in entirely different datacenters so there's no single point of failure. You'd want the datacenters to be in different jurisdictions so that no one country could shut them down. You'd probably reference the IP addresses of these machines by domain name, so you'd want domains from multiple TLDs so that no one domain authority can take over all of your domains.