Use of small refrigerator as humidor

Depends on your environment.  You'd be wise to never turn it on, so if you are in a place where it'll get above 73*, it's no bueno.

I have a dorm fridge in my basement and it's full of boxes, and I use some kitty litter beads to keep the humidity in a good range.  If the seal is good on your unit, and you can keep the temps down without plugging it in, it'll work just like a cooler.

In my opinion, it won't matter in such a small contained space.  It depends on who you ask, but I say humidity in there will seek it's own level, and there's no real need to let the cigar air out and basement air in.

For something of that size I feel fans are not necessary, if you are concerned about air exchange just "slam" the door closed every so often.  That will do the trick.

I use a dorm fridge with Boveda packs for a humidor. Its in my den and it maintains temperature pretty well. I love it and so far I haven't outgrown it. I open the door and check the RH about once a week. If Im smoking more often I don't bother because there is an air exchange every time I open the door. It holds 65%RH perfectly and all my stogies seem happy in there.

I put in some pieces of Spanish cedar because I had them. This is an old pic but yOu get the idea.

 I don't know if my has any Spanish Cedar in it...  mainly because I don't know if any of these boxes are made out of it. 

That's beautiful, man...........