1/Condensers can leak through stone chips also made of alloy, which with salt on the roads can be eaten by corrosion and perforate.
2/If you open the system or replace a part of the system, good practice is to replace the drier component before dehydrating with a vacuum pump. Something a kwik fit company type wont do.
3/ Compressors are an open drive unit , running off an auxiliary belt. They have an open end, hence the name and have a ceramic/ carbon seal to prevent refrigerant leaking, but they dry out through lack of use and it can leak, hence the requirement to run it regulary.
4/ Climate control is just a system to give more precise control of temps. Its no different in the mechanical workings under the bonnet, just motors and flaps under the dash.
5/ Car systems are not great at holding refrigerant. They have flexible rubber hoses in areas of vibration , which is like any rubber item, can weep over time.
6/ Unit behind the dash is the evaporator , which is a very unusual item to leak as runs on lower pressures, but not infalliable.
7/ Running your aircon all the time is like your fridge at home. When it gets to temperature, it will disengage the compressor and not use energy or consumption .
Hope that answers a few more questions 😀