Single-forest,single-domain model Active Directory FSMO design

Hi All,

We are about deploy one Active directory 2k12r2 across 7~8 offices across continent and manage all with OU's

As for Active Directory deployment plan we want to put pair of Active directory servers on 3 locations and the rest with RDOC servers across all offices.

My QUESTION In terms of FSMO  deployment should we put all roles in one location/server or there any best practice for such given scenario?

Please advice

Thanks