Minimum space required for bare 3.0.2 ATV1 operating system drive

Hello

I’m planning to replace the HD in my ATV1 with an SD card for speed and low heat.  I’m going to use ATVCloner to clone the 320GB HD I have in there now to an SD card.  

Does anyone know the bare minimum space required for the ATV1 3.0.2 operating system drive with the fractory minimum installed functions? 

Thanks