What's the best practices of restoring from Stage to Prod


I want to know how to do the backup/restoring between stage and prod efficiently, in the situations below.

1. In A multi-site, develop in a sub-site(stage), when it is ready to go live, how to copy it to the Prod sub-site or the main-site?

2. I develop a sub-site in my local PC (sub-directory), and I want to copy it to a really sub-site of a Sub-Domain Multi-sites in a server. Is it possible and how?

3. How to copy a complete multisite from a domain to another domain?

4. Single Site WP to Single Site WP. When we develop a single site WP, what’s the best practices of the development? Let’s say, 1. develop in local PC then go live to a server; 2. develop in the server then go live there.

Thanks and BR