The golden resolution for inkjet printing has long been 300dpi, though many will argue for 360dpi for Epson printers. Now keep in mind that that is the resolution of your print size, so obviously the film will have to be scanned at a higher resolution to be enlarged to 16x20. For a 16x20 print, you want a file that is 4800 pixels by 6000 pixels. For 4x5 film, that means scanning at 1200 dpi. *You'd actually want a little more since the image area is not the whole 4x5 inches.

Personally, I scan as high as the scanner allows, so 4000 dpi on my Howtek Drum Scanner. Hard drives are cheap and computers keep getting faster. I'd hate to put all the time and effort into perfecting a file and then wish I'd scanned at a higher res some time down the road.

I've never had a DVD or CD go bad, but all the experts say that these are NOT stable media. Hard drives are a little scary too (I have had some of those go bad) so redundancy is imperative. Most commercial operations have double redundancy, so 2 backups of the original. My next investment is going to be an LTO tape drive for archiving off site.

HTH,
CB