祝你生日快乐(zhu 4 ni 3 sheng 1 ri 4 kuai 4 le 4) This is the way we say it But direct translation from English will be 快乐 生日 祝(this word literally means wish rathar than to) 你

寒いis refering to temperature. 冷たい for feeling, touch, such as drinks. As you say 暖かい is an oposite to 寒い、温かい is an opposite to 冷たい. So now you should be able to tell the differences then,

Hi is equvilent to "Hai" in pinyin. One thing I wanna point out is that we really don't ask how are you as often as it in English.

I think the stucture more close to English even though the order sometimes could be very different. But there is some particals in Chinese as well, just not as many as in Japanese. For example, の＝的. It is the connecting words of two nouns. On speaking of the order of sentences, I think Japanese is very different from English and Chinese. In both English and Chinese we say"I go to ". But the direct translation of わたしはがっこうへいきますwill be "I school to go". Or maybe there are ways you could express by using the same order as English and I just don't know it.