Everything Michael said - you are the decider of what is sharp enough (which depends on shooting issues too - lens and camera quality, use of a tripod, etc).
Grain characteristics are all over the place, and depend very much on developing techniques as well, and, in the end, up to your tastes.
As Fred Picker use to say, "Try it, try it, try it. . . "
Regarding large print quality, remember, you don't have to make a 16x20 print to test the quality, just raise the enlarge and make an 8x10 from a place that shows you the qualities you are looking for.