Best Practices for Environment over 15k machines

Hello Guys!!!

We are planing a SEP installation for over 15k machines.

I need to want, how it the best way to do it...

How many SEP Managers is needed?

How many SQL Servers is needed?

Which features should I use? Failover Active X Active?

I have no idea if the branches is connected with the core, or each branch is single

We can suppose 3 scenarios:

 - All branches and HQ are connected

 - All branches are separeted

 - Some branches are connected, and others are separated.

Is there any other thing to take care?

Thanks!

Diego