1) Yes, after completing the post-fixer water wash, submerge the film in a solution of PhotoFlo and water. Follow the instructions on the bottle for correct dilution (e.g., for Kodak PhotoFlo 200, it's 1 part concentrate to 200 parts of mixed solution). Do not apply PhotoFlo concentrate directly to film.
2) If you're using passive drying (i.e., no forced air or heat), it'll generally take a minimum of 90 minutes for film to adequately dry at 20 degrees C and average humidity. Your film isn't dry after only 15-20 minutes -- it may look dry, but the gelatin is still wet.
3) Regarding the dust that gets onto not-quite-yet-dry film, it'll have to be rewashed in water and gently wiped clean (e.g., with your fingers), then re-rinsed in PhotoFlo. The problem in that scenario is that the dust has become stuck -- embedded, really -- in the gelatin of the film, so a simple brushing or blow from an air duster won't dislodge it.