The air cargo market is defined by the transportation of high-value, often specialized goods, requiring precise handling. From a planning perspective, air cargo operations involve complex, nested decision-making across multiple levels. While previous research has addressed fleet assignment, cargo routing, and air cargo load planning as individual problems, few studies attempt a fully integrated approach. This work presents a comprehensive model that jointly optimizes fleet assignment, Unit Load Device (ULD) routing, and cargo allocation to ULDs within a full freighter network. We propose two solution methods: a sequential approach and an integrated approach. The sequential approach first performs a myopic fleet assignment and cargo routing, treating each aircraft as a single bin without assigning cargo to ULDs or routing ULDs. These tasks are then addressed in the second stage, ensuring compliance with bin-packing and compatibility constraints in the final result. In contrast, the integrated approach employs column generation to optimize all routing and packing decisions simultaneously. Both models were tested on synthetic instances based on a major European combination airline's freighter operations. Results indicate that the integrated approach consistently outperforms the sequential method, achieving profit increases of 6-24\% across various operational scenarios. This improvement is driven by the ability to yield higher revenue while lowering ULD operating costs.