回答
(1)
missing をよく使いますが、他に absent, nonexistent, lacking などがあります。状況によって使い分けます。
The most important information is missing from his email.
The animal had fingers, but fingernails were remarkably absent.
A kitchen is nonexistent in our office building.
A good strategy is lacking for his team to win. His team lacks a good strategy.
しかし、日本語で「不足している、足りない」というのは、英語では need や require を使うことが多いです。つまり、足りない状況を述べるのではなくて、「必要だ」と断言するのです。
We need the information included in this report.
We need a small kitchen in our office building.
His department requires strong leadership to complete this project.
We needed his participation in this meeting. He was absent from this meeting.
(2)
おっしゃる通り、short です。他に、insufficient, inadequate などがあります。目標にかなり近いときには shy も使えます。
The shipment was 500 pieces short.
We have an insufficient number of people in the engineering department.
Her interpersonal skill is inadequate for the sales job.
Our production today was just 10 units shy of the target.