Six hundred dots per inch, because you will not do this twice
Resolution
Six hundred for prints and twelve hundred for negatives and slides. Storage is cheap and rescanning a box of photographs is not.
File format
TIFF for the archive copy and JPEG for sharing. JPEG loses information every time it is saved, which matters over decades.
The metadata
Write who and when on the file at the time of scanning. Nobody comes back to do it later and the knowledge disappears with a generation.
