I've never had a problem with just putting the tobacco into jars, screwing down the ring, and letting time have its way with the stuff. Not only is there no reason to heat them, or go to any other lengths, I'm actually convinced that heating the tobacco may not be optimal for it. If the manufacturer wanted the tobacco stoved, it would have been made that way. (There's an article in the Chronicles about some
Odyssey that had been heated this way, and how it compared after just a few years with some that was not.)
And, remember that because of the way microwave ovens work, the internal temperatures of the tobacco are likely to be significantly higher than what you are feeling. Once those water molecules set about their high-velocity square dance, you're getting some serious heating.
As to washing the jars, though they're sterile when they're packed, they are picking up airborne spores, yeasts and bacteria when they're sitting around. It's
probably okay to use them as is, but I prefer to be safe, and do a hot water rinse, followed by drying and cooling them upside down on a rack.