there's a website names 网易公开课，http://open.163.com/cuvocw/  this is the link of the website. You can find the courses which are given by the Chinese teachers from different universities on various topics, mostly in Chinese(Mandarin).

About the four Chinese musicians you mentioned, I personally like Khalil Fong and Li Ronghao most. Just like you said, Khalil Fong's songs are mostly R&B. So I am fond of them because they're relaxing. As for Li Ronghao, some of his songs are really fantastic. And he is also a good songwriter. He had wrote some songs for another Chinese musician who's name is Xue Zhiqian. I highly recommend you to listen these songs if you had time. And I hope you will like it.

check please

I wrote it from a voice

1 你怎么了？- 生病了
2 他正在做运动
3 爸爸每天都要喝杯咖啡
4 生日快乐，这个送给你
5 别玩手机了，和我去打篮球吧
6 快去洗洗手，来吃苹果
7 我不想听你说话
8 看，我新买的桌子和椅子（No Space Needed）
9 没想到外面这么冷
10 介绍一下这是我妻子

We Chinese put the punctuations marks in the bottom of the characters. For example,你好。

《《 最近 》》

你们最近在做什么？我今天吃了月饼。很好吃！我这里是星期五，你们那是星期几？你喜欢星期五吗？你们星期五做什么？你会去参加派对（party）吗？

Are these sentence correct?

1- 张文在哪里工作？Correct 
2- 张文工作很忙吗？Correct 
3-每天要多少小时工作？

每天要工作多少个小时？

4- 有时候一个星期要工作几天？

一个星期通常要工作几天？

I don't know your exact meaning by saying "有时候"，if you want to express "How many days does he work in a week as usual?" Then you can use 通常

5-今天下班以前经理告诉他什么？Correct

6- 张文可以休息多少星期？

Correct 
7- 张文准备去哪里旅行？

Correct 
8- 坐飞机要多少小时去西安？

去西安坐飞机要多少小时？

Or 去西安要做多少小时的飞机？
9- 坐火车要多少小时去西安？

去西安坐火车要多少小时？

Or去西安要坐多少小时的火车？
10- 张文想坐什么去？

Correct
11- 回家以后还有几天？

What do you mean?

If you want to say "After how many days will he be home?"

then the correct Chinese should be:

他还有几天回家？
12- 他可以走什么在那天？

If you mean On which day can he leave ?

他哪天可以走？

13-如果你到中国朋友家去做客，应该怎么称呼朋友的家人？

朋友的爸爸：叔叔

朋友的妈妈：阿姨
14- 到朋友家去做客，要不要带礼物？

为了表示礼貌，最好带礼物。
15- 应该带什么礼物去？

视情况而定It depends.