The smallest and least would be "minimal" in Engpsh. This comes from the Latin word "minimus," which means "very small" or "least." Here are some example sentences in Engpsh and their translations in Chinese:
The minimal amount of time I need to prepare for the presentation is one hour. (我准备演讲所需最少的时间是一个小时。)
We only need the minimal amount of furniture for the new apartment. (我们新公寓只需要最少的家具。)
The artist used minimal colors in the painting to create a more modern look. (艺术家在绘画中使用了最少的颜色，以创造更现代的风格。)
Minimal can also be used as an adjective to describe something that is very small or has only the bare essentials. For example:
She wore a minimal amount of makeup to look natural. (她化了很少的妆，看起来很天然。)
The room had a minimal amount of decor, with only a few pieces of art on the walls. (房间里只有最少的装饰，只有几幅画挂在墙上。)
Overall, "minimal" is a useful word to describe something that is very small or has only the bare essentials.