@Karen Taylor good question, and yeah your instinct about line-of-sight is correct — that 50km figure is drone-to-drone with both modules elevated, so ground reflections are out of the picture entirely. For ground-to-ground you're looking at closer to 5km, which is still pretty exceptional for BLE.
On the RF front-end question: the module already has the external amplifiers and receiver sensitivity optimization built in, so you're not starting from scratch like you would with a raw Nordic or Silicon Labs chip. That said, your PCB layout still matters more than people expect at 2.4GHz — keep your antenna keepout zone clear, avoid copper pours under the antenna section, and make sure your power supply isn't injecting noise into the RF chain. A dirty 3.3V rail will hurt your sensitivity floor regardless of what filtering is on the module itself.
If you're in a particularly noisy RF environment (near switching regulators, motors, or other 2.4GHz devices on the same board), a ferrite bead on the power line to the module is cheap insurance. External SAW filtering on the signal path is probably overkill unless you have a specific interferer you're trying to reject — I wouldn't add that complexity without a reason.
What's the rest of your board look like? If you've got motors or a switching regulator nearby that changes the answer a bit.
