they can understand you , but it sounds very strange. use correct nouns is better.

They will understand you since you are foreigners. But it really sounds a bit strange. According to the grammar rule of chinese mandarin, we usually use different measure words to modify different objects. such as 一棵树，一条裤子，一件衣服，一碗面，一盆（朵、束）花 etc. I hope it helps. :D

No you can't. Many nouns need special measure words instead of 个.

像" 个，只，头，件， ..."这些词，在汉语里称作为量词。什么时候使用那个量词是个习惯搭配的问题,不必在乎它们之间的差别。比如说，一只鸡，一头牛，一件衣服，一套装备，这都是固定用法。你记住，就行了。

you need to learn different measure words such as " 个，只，头，件， 套..." just more practice.. i'm sure u can handle it.