My company investigates these types of problems on a daily basis (I'm in Mich - similar climate to NJ). I was in a house yesterday with 82% humidity!! That house was on a crawl space - the number 1 cause of moisture/mold problems by far.
One of the problems in the first few weeks of the heating season is residual moisture built up in the building materials. This is particularly true in homes without central air conditioning - all that summer humidity is absorbed into the drywall, carpets, insulation and lumber. It takes several weeks for the building materials to 'dry out'. We always have a rash of moisture/mold investigations during November and December.
Although you will see published data indicating "normal" indoor humidity levels as high as 60%, our experience has been to keep it below 40% .... as far below 40 as it's comfortable for you.
Also, by keeping the door closed in your bedroom, it will generally be cooler than other rooms - particularly if its located over an unheated garage. Cold air holds less moisture and moisture will condense out of the air onto cold surfaces such as the walls. With hot water radiant heating (a good type of heat BTW) you don't have the benefit of air circulation blowing around to dry out this surface condensation and mold will eventually grow. You might want to consider a ceiling fan in the bedroom and run it on low continuously. Air movement is good. And get that bathroom fan installed and vent it directly thru the roof, not into the attic.
