With Windows 10 you'll find that *most* of your existing GPOs created with the Windows 7/2008R2 GPMC/administrative templates will work just fine. Although you won't be able to manage the newer features added in Windows 10.
Microsoft thankfully provide the newer administrative templates for download in MSI format so you can manage Windows 10 specific settings on non-Win10 machines. What I'd personally recommend as I've done it in our environment, if you haven't already, is to create the Central Store for ADMX files in your domain. This means you can replicate ADMX files across your domain controllers and have access to the same set of templates on any computer running GPMC.
My advice upon creating the central store is to download both Windows 7 and Windows 10 ADMX packages and install them. Copy the Windows 7 ADMX collection into a new temporary folder (skip any of the Language Code folders apart from en-US unless you require them) and then copy the Windows 10 ADMX collection into that same new folder (overwriting the changes). Then copy the folder containing the new files into your \\domain.com\SYSVOL\domain.com\policies\PolicyDefinitions folder you created when setting up the central store. This means that you retain any Windows 7 specific ADMX files that were removed in Windows 10 and have the newer Windows 10 GPOs available too.
Here's the Microsoft article with links the ADMX templates and information on setting up the central store.
