The future of wireless communication requires the unique capabilities of free-space optics (FSO). Therefore, it is crucial to develop methods for achieving reliable long-distance FSO communications. This article presents a field trial of a 1.8 km FSO link that can achieve 4 Tbps+ using coherent optics, wavelength division multiplexing (WDM), atmospheric turbulence mitigation, and optimized forward error correction (FEC) coding. Our study focuses on the impact of atmospheric turbulence on FSO communication and the methods used to mitigate its effects. We compensate for the turbulence-induced power fluctuations by using an optical pre-amplification technique with automatic power control (APC) to stabilize the received power. This technique reduces the perceived Rytov variance by a factor of ten, making the FSO communication more reliable and efficient. Furthermore, we explore the maximization of net bit-rate by optimising the transmitted channels' FEC overhead, considering two different architectures: individual and joint wavelength processing. The proposed optimization techniques are shown to provide significant gains both in terms of capacity and reliability, making FSO technology a more practical solution for long-range wireless communication.