I should actually grab my pi4 (2gb) as why I am trying to build on a Pi3A+ is a mystery to be honest and is the definition of pain 
There is a lite version now of the 64bit of raspios https://downloads.raspberrypi.org/raspios_lite_arm64/images/raspios_lite_arm64-2020-08-24/ 3 even if still a beta its likely to end up a datum distro for Pis.
Debian is fine but guess you will be building 1.6 so might wait.