Maximum number of SSO servers?

Hello,

We have a vSphere deployment with 13 remote sites and 1 central site.

We want to setup local vCenters + ESXi clusters on each site, but with Single-Sign On and with linked-mode vCenters to the central site vCenter.

The central site will also have a vCOPS instance monitoring all sites.

So 2 questions:

1) what is the maximum number of SSO servers that we can install? We need at least 13+1=14.

2) what is the maximum number of vCenters in 1 linked mode group? We should also need 14. I read in the vsphere55 Config Maxima that this is set at 10. Is this a hard-coded or soft limit? Anybody has experience with this amount of linked mode vCenters?

3) If the limit is really 10, what do you suggest to put in the Central Site so as to have a single-pane off glass management and monitoring?

Thanks in advance,

Francis