Also if you dont have it somewhere away from the cold as the temp changes it will have condensation form possibly and that too will cause quick rust .....I found out the hard way :P Dry location if possible,even if it gets cold, as long as you can keep some air circulated on it till you get ready to paint .
I would just chase the threads with a decent tap and some tapfree, I don't know about masking the vin. I had a base/clear paint job on mine and the vin is almost unintelligible, my guess would be powdercoat is as thick.
A lot of folks will actually spray the entire frame with WD40 until they are ready to paint it. Just needs to be spotlessly degreased before painting.
Many drag racers actually keep thier frames raw steel. This allows them to see any craks much easier than if it was painted. they just spray it with WD40 about once a week.
Desert racers do the same thing. When I lived in SoCal, I had a buddy with a rock buggy that kept the entire frame bare steel. After a weekend in the desert, he would power wash it, let it dry, then wipe it down with WD40.