I would run the two systems in a parallel mode (SAV AND SEPM) - start with your central site.
Make 2 or 3 SEPM servers and use SQL. So you have the load and fail thing enabled at your central site (HQ) and maybe make a couple of other sites with SEPM servers. But do not make to many.
Use GUP instead if you have under 200 clients at a remote location or LU if you have more. There are a guide to LU on cd2.
After you have done the setup of SEPM, start migration a couple of client to see that it is working, especial if you are using the firewall and application control thing.
We will have 3 sites, one in emea, america and asia. 2 of those will replicate logs to the HQ. At the moment only the HQ site is running.
I was also a bit puzzle in the start, but after I read that design guide and the admin guide I could see the light (almost) :-)))