Maybe there was once "plastic" and now there is "plastic" but it's different plastic Seriously the modern transparent and genuine neg files like "Clearfile" are fine but yes never put wet negs in such files. It is always worthwhile to run the insides of your fingers up and down the roll after drying. If there is any wetness your skin will detect it. The film should feel as smooth as the baby's proverbial before inserting it into a neg file

As far as measuring is concerned switch to metric instantly and no more confusion. I bet your fellow Canadians in Quebec are metric as sensibly all our European neighbours are and we in the U.K. are getting there rapidly

Vive Napoleon!