1. No, in Cantonese, 打工 usually, but not exclusively, refers to full-time employment. e.g. 你鍾意做老闆定打工呀？(Which do you like, being a boss or being an employee?)
2. 工夫. Beware of the difference with 功夫 (kung fu).
3. Both have the second tone.
4. Without further context, it is impossible to determine if the sentence is in past, present or future tense. Suppose it is in past tense and 佢 refers to a man, then 我介紹你識佢 means I introduced him to you. Literally, I did an introduction for you to know him. On the contrary, 我介紹你畀佢識 means I introduced you to him. Literally, I introduced you for him to know you. However, 我介紹你畀佢, i.e. without 識, implies that the introduction may aim at something more than just knowing each other. For example, I introduced you to him to see whether he can employ you or use your service. Whether this implication is valid depends on the context. In fact, you can specify the purpose of the introduction by saying e.g. 我想介紹你畀佢做助手(I would like to introduce you to be his assistant).
5. It is too simplistic to say whether they are grammatically correct. We usually say 一千個人, 一千人 or 千人. They all mean 1,000 people but 一千個人 is more common in daily conversations and 千人more common in written materials. 千個人 as such is less common but it exists in sentences such as 嗰度有成千個人(There are as many as one thousand people). This is due to the term 成千(as many as one thousand), which is, like 成百(as many as one hundred), commonly used, rather than the term 千個人 itself. I hope I am getting my point across.
6. In Hong Kong Cantonese, the term 早飯 is not used. I guess it might be used in other Cantonese speaking regions of Guangdong.