You need to launch ROS and MAVROS, in the PXFmini image is not activated/launched by default at boot. ( So it does not consume resources, notice that the RPi Zero has just a single core @ 900MHz)
You already have one
catkin workspace in the image, go to
/home/erle and check the folders.
You don't need any, the barometer should give you altitude readings. But if you want to use autnomous modes of flight you need GPS (as said in quite a lot of posts about ROS teleoperating in this forum , check them out to make an idea about what you need software-wise )
ROS is the infrasctructure, it does not contain any command to create packages. MAVROS is also installed in the image.