1)我先举个例子:
There are differences between A and B.
这里A和B都是名词成分。
同理,你的句子中,how many goods people want to buy整个也是名词成分,不是定语(形容词成分)。
2)people want to buy即是goods的定语从句,先行词被省略,不是宾语从句。
3)可以看一下下图的定义
词典指出宾从是动作的对象,
比如I know he is right. he is right就是宾从。因此你的句子中how many不是宾从。