I got 2 cents to add.
I don't scan negs for the APUG gallery. I scan 8x10 prints. My scanner is the Epson 4990.
The preview scan is cropped to the image with no border. My thought is the border will add non image white to the overall balance. I remove Epsons' presets and scan at 560 dpi.
In my Photoshop Elements (Not real Photoshop) I change the mode to Gray-scale.
I use the auto contrast function which 99 out of 100 times serves me fine.
I re size the dimension to 8 inch hi and let the width fall where it may.
Then I begin a reducing process suggested by JD Callow a few years ago:
Unsharp masking: At the 560 I set % at 50, Pix at 8, Threshold 5.
Adjust dpi to 1/2: At 380 I set % at 25, Pix at 4, Threshold 10.
Adjust dpi to 1/2: At 190 I set % at 12, Pix at 2, Threshold 20.
Adjust dpi to 1/2: At 95 I set % at 6, Pix at 1, Threshold 40.
With each adjustment you may wish to change you view to Screen Size.
Go back to the Re-size box and set the Vertical dpi to 600.
Save for Web and upload.