I'm guessing that if you wanted to print these up at around 24" high x 68" wide a scanning DPI of 1440 would be fine, or potentially scan a little higher and then downsample to 1400 DPI. I guess the file would still be huge though.
Dust isn't my problem - it's drying marks and what appears to be over-enthusiastic wiping. The latter has left some of my negatives looking as though they have been cleaned with a Brillo pad...
I went through several labs claiming to do B&W. One made me wait several weeks because he only had one type of some equipment that was being fully utilised with his colour work. Another made me pay extra for push processing and then didn't do it.