What is the difference between honesty and too much information? (Possibly NSFW)

No difference. It is difficult to compare the two. Honesty is always the best policy but some things are better left unsaid. One could tell all there was to tell but it would be like cutting off your nose to spite your face.
“The better part of valor is discretion.” Shakespere’s “I Henry IV.,” v. 4. 121

“Honesty is praised and starves”
Juvenal

Only on a need to know, otherwise leave it.

They mean quite different things. If they seem so related that this question seems to make sense, then that’s really because of some social context that makes it so, not about some intrinsic property of honesty or information.