Many thanks for testing Raspbian Buster. I was just about to create an image for RPi (Buster image) but then we needed to fix those nasty ARMv6 errors with the last update quickly.
However yet manually changing the sources.list (and sources.list.d/raspi.list) is the way to go. Debian mini.iso does not work since this is Debian, not Raspbian, which does not support the RPi without having it's custom bootloader+kernel installed first. For this reason we use the Raspbian Lite as base image (sadly only Stretch available so far) and do a dist-upgrade as well.
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