I'm still very iffy about these rules. However, a lot of that is because I'm having trouble understanding how drones fit into this equation. Part of that is I don't really understand upgrading sensor systems for drones.

If I upgrade the sensor systems for a drone to give it Low Light, Thermo, Vision/Audio Enhancement and so on, do they increase the sensor channels for a drone?

Yeah. A drone with LL, Thermal, VE, and AE would have 4 sensor channels, and so be able to help out with a rating 2 tacnet Actually it would have at least 6, because it would also have normal visual and normal audio as well.

Basically 'sensor channels' is 'how many senses/sense improvements can you provide'. A camera is 1 for visual. A night vision camera is 2, 1 for visual and 1 for night vision.

Simple enough. Thank you.

Is there anything I have to do to add the enhancements to the drones beyond just paying the enhancement costs?

I think drones of different sizes can only support so many types of sensors. Should be in the sensor section of the main book and I think it expands on it some in Arsenal. Don't remember all the rules off hand, and I think you can do stuff like get a camera for 1 sensor slot and then add all the vision mods to it directly.

So I have a question--does 1 sensor capacity= vehicle mod slot. Most drones only have 4 vehicle mod slots.

No, sensor capacity is entirely seprate from vehicle mod slot.

BBB 325 has the sensor packages.
Arsenal 105 gives the typical pre-installed sensor package for at least a vehicle.

I'd say in the standard 8 capacity for a large drone, you could easily enough drop 8 channels worth of sensors in, especually with therm and lowlight on the cameras.