I just need some confirmation, before I break something. So far I have been powering my project from USB, no I would like to power it from a battery. The official spec claims I should use a voltage anywhere from 7-12V, so I got myself a 9V block battery and would connect the positive lead to the VIN pin and the negative lead to the ground pin right next to it, based on this schematic: https://40.media.tumblr.com/cdadca4e95808b376de52a88a5468367/tumblr_mi61oww6cu1s5t695o1_1280.png Do I need a resistor?
According to this schematic, VIN goes to the on arduino-micro's 5 and 3 volt regulators. So you should not need a resistor.
The 5 volt regulator needs a bit more than 5 volts at it's input to do a good job. That is why the specification calls for 7 to 12 volts.