My advice, if you're going to go thru the trouble of scanning the original slide, is to scan as LARGE as you can the first time, and ALWAYS save in TIFF format. Everything else can flow from there.
So far, so good.
I can store approximately 80 such TIFF files on one DVD-R.
Hmmm... where they will keep for perhaps 30 years before the substrate degrades. Assuming one can still find DVD players and software to read them 30 years from now, which I have my doubts about...