が必要 => need; necessary N4
必要がある => Need/Need to N4
必ずしも~とは限らない => Not necessarily; not always N3
~はめになる(~羽目になる)     => to get stuck with (some job); to end up with (something unpleasant) N1
[必要「ひつよう」]はない => It is not necessary for A to be done N2
Needs, Requirements