If a site is involved in more than one study, do I need to create multiple instances of the site?

No. You can create a site in a study, and then you can add it to any other study without having to re-enter details about the site.

When you add an existing site to a study, you can change details about the site for the study without affecting the site in other studies. For instance, you change the address or phone number.

Additionally, a site can have different statuses in each mode. For example, a site can be Active in Testing mode so you can verify a study and New in Production and Training modes.