To setup subinterfaces just use the name of your interface and add _1 so internal becomes internal_1, internal_2.
For the VPN you have to create a VPN community.
Mesh is used for VPN between all devices, Star topology is used to create a VPN between the center gateways and the outer gateways. You can define these in the Dashboard ofcourse.
For the routing you have to adjust the routing table of the OS. Simple as that. Do keep in mind to define your topology correctly in your Dashboard.