Hello,
MS-MIC (and MS-MPC and MS-DPC) t'put is the sum of all traffic passing through in all directions on all subinterfaces.
Taking Your diagram as example topology, You can have as a maximum:
1/ 1Gbps down and 8Gbps up, spread across all MS subinterfaces
2/ 2Gbps down and 7 Gbps up, spread across all MS subinterfaces
3/ 3Gbps down and 6 Gbps up, spread across all MS subinterfaces
. . .
XX/ 8Gbps down and 1Gbps up, spread across all MS subinterfaces
The max number of MS subinterfaces You can configure on MS-MIC is in order of several thousands.
Normally, when You do interface-style services, You have 1 subinterface.
Normally, when You do nexthop-style services, You have 1 "inside" subinterface and 1 "outside" subinterface, marked as such in the configuration. In certain cases You can have >1 "inside" subinterfaces mapped to 1 "outside" subinterface when doing i.e. IPSec at scale.
Interface-style and nexthop-style service-sets are described in this book https://www.juniper.net/uk/en/training/jnbooks/day-one/networking-technologies-series/cgnat-up-runnning-mx-series/ , chapter 1.
HTH
Thx
Alex