Load Balancing & Fault Tolerance - Territories & Gat

Can anyone briefly explain about how load balancing & fault tolerance be attained using multiple brokers, Territories and gateways?.

Say suppose we are integrating Application A and Application B.Its basically synchronization of data between the two applications. In this we
have an Application A Outbound model and an Application B Inbound model. As of now we have only a single broker which handles all the documents flowing between both(Outbound and Inbound) the flows. Do i need to have a separate
broker for each model, say one broker for Application A Outbound model and another broker for Application B Inbound model in the same territory.Or do i need to have two territories one for outbound model with a broker and one
for Inbound model with another broker?.