Quintum Setup PBX and International

Hi, I recently acquired to AS FXS/FXO boxes and I will like to configure as follows :

a) both boxes will be within a private network. They will be connected to a PBX using the extensions FXO port.
b) On each I need to make them call each other using extensions. For example, dialing 111 reaches gateway “B” and gives me a second dial tone, I will dial now the second extension number at pbx “B” to be able to communicate will people at location B
c) I also need to place calls internationally using a voip partner using quintum / cisco.
d) Is a cdr server sufficient for both gateways or I need to use a separatee one for each gateway ?

Can someone provide me some light as to how I should configure the boxes. As of right now, I am confused with what is a border element, and the dial plan. In addition, this configuration will grow in the future because I will add more offices.

Lets say i put this is a company,

what will i need to charge them for each call placed ? do i need another gk, gw to control the outgoing calls for international service ? or can this all be configured in one side.

Your help is appreciated.