SCCM 2012 Design and Management

Question

I'll preface this by saying I dont have much experience beyond setting up a stand alone primary site for SCCM 2012. 
Here's the situation:
1. Central Office in LA, CA with smaller offices in Texas and in SF (totaling about 4k clients)
a. Fast 10G link to TX
b. Slow link to SF
2. Korea office with 500 clients (slow link)
3. Europe office with 1500 clients (slow link)
4. Local IT staff managing systems and software deployment in each location. 
5. Central office would like oversight and management of other regions. 
If anyone could provide suggestions on hierarchy design that would be appreciated. 
Originally I was going to setup a CAS and a Primary Site in the US (DPs for SF and TX), and 2 other Primary Sites for KR and EU regions (Remote DPs and what not for the smaller branches within). IT staff for each region would manage their own primary. But this
apparently isn't ideal. 
My question is how a stand-alone primary design would work in this instance? And if the primary resides in the US, would administrative users have to use the console to access the primary over the slow WAN link?
I think my confusion in design comes from whether the regional admins need direct access to the Primary site or not. 
Thanks, and please excuse my ignorance. 

Answer 1

I'm not sure what the internet cloud is there for.  Your LA Primary should be in that spot; remember those servers all need to be able to communicate with the primary, usually on the same domain.  If what you meant by that 'internet" cloud
you really meant "Our Internal Company WAN Links", then ok.  By that I mean... I presume in SF, KR, EU... there are domain controllers servicing those locations?  then it's sorta similar to CM12.
If you really *do* mean internet is how those locations are linked, no domain trusts, then what you may be looking at is pki certificates, and internet based client management.  And/Or possibly considering leveraging Intune for those clients.
Regarding console usage; either publish the console via Citrix, or publish the console as a TS App.  i.e., publish the console from citrix via a citrix server in the same datacenter as the LA Primary--and everyone uses that console (if they need to
use the console). 
fyi/off topic... my opinion.  "helpdesk" type personnel have no need to be in the console, nor does anyone who simply needs to run reports.
Standardize. Simplify. Automate.
Correct, internal WAN links, all computers are domain joined. We will eventually move to internet management too but that seems to be something we'll tackle later down the road. 
I will need to check with the other admins to see what kind of VDI we have in place. 
Console access is for other admins to create/modify collections for their region, deploy software, etc. The console itself wont be made available to helpdesk/service desk.
response to edit:
- Correct, TX will only have a DP on a "site server" (not a secondary site). 
- link to SF would be 1GB, and change to 10GB once they move into a perm location. In my diagram they would also just receive a DP
edit 2: ok my vocab is off, when i put "site server" in the diagram i really mean "site system server"