Word to explain "the exact required quantity" neither too much nor too little

Solution 1:

I think the adjective Goldilocks may fit your criteria

[AS MODIFIER] Denoting or referring to the most desirable or advantageous part of a range of values or conditions (typically the center):

the planet is in the middle of what astronomers call the Goldilocks zone: a place that’s not too hot and not too cold

he promises us a return to the Goldilocks economy—not too much deflation, not too much inflation

Oxford Dictionaries Online

The term derives from the fairytale about a little girl named Goldilocks and her encounter with three bears. The modern versions recount a girl who breaks and enters a home and keeps sampling the possessions of the mother, the father and the child, choosing, for example, a bed which is not too soft, not too hard, but just right.

The term has now been adopted into a phenomenon often referred to as the Goldilocks principle and the Goldilocks effect

The Goldilocks principle states that something must fall within certain margins, as opposed to reaching extremes. When the effects of the principle are observed, it is known as the Goldilocks effect.

Solution 2:

"going into details precisely as much as it is needed, not more, not less..."

precisely adverb: exactly (used to emphasize the complete accuracy or truth of a statement). "at 2:00 precisely, the phone rang" (Google)

Or perhaps, proportional (or both combined),

e.g., going into details which are precisely proportional to the need, not more, not less...

proportional adjective: corresponding in size or amount to something else. (Google)

Solution 3:

The neatest answer, usually lower case, is

q. s.

(Wikipedia)