I use the same paper that you use and a similar print dryer (an older Arkay model). You should definitely wash the canvas. This will help with your fiber problem. Also, since it's used, you don't know whether there is any residual fixer on that canvas that could adversely affect your prints. You should put it back on the print dryer before it is dry and turn on the print dryer to dry it. This way it will not shrink.

My FB prints will dry relatively flat, but I still need to dry and flatten them further in a dry mount press between sheets of 100% cotton rag mat board.

The look of glossy FB paper is supposed to be what you are getting - sort of semi-gloss. Some people don't like this, but it is considered by many to be the paper of choice for fine-art B&W photography. Good luck!