Never apologize for a question you ask because the question you ask, however basic it may seem, might be the same question someone else is afraid to ask! Plus, we all started out new at one time or another.
Finding a way to identify what country a device is in is key here. That can be via the user that's assigned to the device or it can be via an Extension Attribute that you use, but once you have that information in the computer record in Jamf you can then use Smart Groups to collect devices into the proper "containers". From there you can use those Smart Groups to scope configuration profiles, policies, applications, etc. The Extension Attribute way could be as simple as a pop-up EA that allows you to choose the country, either on the computer record in Jamf Pro or via the API if you're so inclined. You can also write to a file on the device to store that information (along with anything else you want) and read it back into an Extension Attribute. The point being, get the country (or however you want to identify where a device belongs) into Jamf Pro and use that to create your groups.
For your Zero Touch deployment, you can have multiple PreStage configurations. While it is a manual process to move devices between the PreStage configurations, you can use two different PreStage configurations to have a device go through the proper Zero Touch deployment. You can then use a Smart Group looking at "Enrollment Method: PreStage enrollment" to gather devices based on what PreStage they ran. This can then be used to scope a specific "Enrollment Complete" policy/workflow for those devices.
Sites can be useful, but they are really for situations where you need to control what a Jamf Pro admin has access to in the console, not for scoping situations. So if your IT team needs to have access to all devices, leave it without using Sites. If your IT team is broken into a California team and an England team, and the two teams should not have access to effect change on the other's devices, then you should look at Sites.
Previously I had a team managing devices across the globe and we utilized a plist file stored on the device to store country, along with other information, and would use an Extension Attribute (using the defaults command) to read in that info.