不知道你的句子来源为何处。据我个人理解，这三个句子，即使不算错，至少不算“好”的句子。

句子1：Not much clothes is needed.

在现代英语中，clothes 是一个没有单数形式的复数名词，可以说 many clothes，但一般不说 much clothes。根据《葛传椝英语惯用法词典》（以下为原文引用）：clothes 是复数形式，没有单数形式。统指衣服，不指一件衣服。可以说 many clothes, these clothes 和 those clothes。但不可说 three clothes 等。现在很少说 much clothes。

所以你的句子在现代英语中，即使不算错，至少属于“很少说”的用法。建议改为：

Not many clothes are needed. / Not much clothing is needed.

句子2：Too much old magazines is on sale there.

我个人觉得这个句子有错，应改为：

Too many old magazines are on sale there.

句子3：Too much fruits is also harmful to your health.

我觉得这个句子不妥，最好改为：Too much fruit is also harmful to your health.

fruit可用作可数名词或不可数名词，但用作可数名词，强调种类，用于此处不是很好。