I have some old micro SD cards that I'd like to use if possible. How much space does Raspbian need and how much room should I leave over? (What is the minimum size card I can use?)
I installed Jessie Lite (2017-03-02-raspbian-jessie-lite.zip) on a Pi 3 with a 2 gigabyte micro SD card. Here's what df showed me:
Filesystem Size Used Avail Use% Mounted on /dev/root 1.8G 846M 807M 52% / devtmpfs 459M 0 459M 0% /dev tmpfs 463M 0 463M 0% /dev/shm tmpfs 463M 6.2M 457M 2% /run tmpfs 5.0M 4.0K 5.0M 1% /run/lock tmpfs 463M 0 463M 0% /sys/fs/cgroup /dev/mmcblk0p1 63M 21M 42M 33% /boot
So it looks like 2G is about the lowest you can go with a stock Raspbian Jessie Lite image.