How cool that you're moving into the format. See, for every one of you a thousand Western Hemisperians move into digital. We're a small group, but we're tough.
Anyway, the scratching comes from the way you load the film into the drum. I used to get this all the time. When you curve the film in your hand to load it, if you curve it over on itself or if you let go of it when it's touching another piece of film, it scratches. It happens pretty easily, apparently.
The blue dot is probably anti-haltation dye that did not wash out. If you wash the film again, for longer, it should come out. If you do not pre-rinse the film sometimes, the dye stays and is stubborn. When you do pre-rinse the film you will see all the dye, or alot of it, when you dump the water before adding developer.
In my experience, changing bags are hard to use and seem to cause dust if there's the least bit of static in the bag. Use a changing tent if you can find one; they make all the difference in the world. To minimize dust, just make sure you both blow with canned air and brush the holders every time you load them. If you got them used, you should seriously blow through the light trap. Light traps seem to also be dust traps.
Hope this helps. Welcome to the format!