Fan Control By Humidistat

I have a need for a circuit that will control a 12vdc fan based on the humidity level. Ideally, this would include a potentiometer that could be set for the desired humidity, along with an LED readout of the current humidity level.
Requirements are: Runs off 12vdc or lower, small package, low power consumption,

I've been poking around forums and have collected some ideas. Please be kind as I'm am not an electrical engineer, or even an electrical student. I've attempted to include a very basic block diagram/schematic.

Here is a very basic block diagram

Think I finally got the attchment loaded.

The are lots of things wrong there.

The main thing I can see is that many components are missing, the LM339 will also not power a relay directly, use the LM311 which can directly drive a small relay (<50mA).

Thanks Hero999

I'll make that change