Bapi,
There are yes's and no's to your questions. Moreover some companies starting with a yes are now changing to a no. High level organizations are something that you do not copy and paste but define according to you company goals, policies and structure.
Nevertheless a can give you a hint on it. If you start for the first time in this business, try a unified core team as a deepwater technology group and fill it with the skills and competencies needed for your short-medium term objectives. Do not make it too much multidisciplinary, so to focus it on what really matters. Work very close (project teams) with the G&G people and then grow from it according to work load and demand. But keep the core centralized until you matured as to concentrate all knowledge and experience. This way you can distribute it to the different locations without dispersing management efforts.
This is how most of the majors started sometime ago. All of us evolved in different manners depending on how this knowledge has been distributed or delegated along the maturing line.
I wish you the best of lucks finding the organization that better suits you. It is not a simple task.