在火车站。

revised version:

- 你好。我要买两张车票去(or到)北京，五月一号星期日14：05出发。火车的班次是G1234。
- 请给我你们的护照。
- 给你。
- 两百块。
- 好的。火车从哪个站台出发？
- 第八个站台。
- 谢谢。

explanation:

(1)两个. Tickets are pieces of paper, and 张 is the proper word for this kind of thin and flat objects. Thus 两张车票 is the proper way.

(2)到北京。It is actually correct. I often use 到 as well. But it can be a little bit confusing under certain circumstances. I will give you two examples to show the slight difference.  Example 1：我想买一张明天下午2点到北京的车票。Example 2：我想买一张明天下午2点去北京的车票。The only difference is 到 and 去。The second example is quite straightforward. It means I want to buy a ticket for a train which is scheduled to depart from this station at 2pm tomorrow and head for Beijing.  The first example can have the same meaing as the second example, but could also refer to a train which would arrive at Beijing at 2pm tomorrow. I was once misunderstood by the ticket seller at Beijing due to the different understanding of 到, so I would like to point it out for you.

(3)星期日1五月：it is Chinese way to put it in this order: 年、月、日、时. So it is 五月一日星期天。In spoken Chinese, both 日 and 号 are used so it can be 五月一号 as well. 星期天 is equivalent to 星期日 and 礼拜天.

(4)号码。we don't call it 火车号码 though it is actually a letter and a number. The common words here include 火车班车 or 火车车次。

(5)月台。It is actually a correct word, and  I guess it is still used in many overseas Chinese communities. However, it sounds like an old expression to me, which you might come across in some books published 50 years ago. Nowadays in mainland we would prefer 站台. You can keep this preference, since it might be still in use many regions and they both refer to the same thing.

在火车站。

在火车站。

出示 : chu 1 shi 4 : to show 

五月一日星期日: month/date/day, when you write a date in chinese, you need to respect this order, like in English. 

第八号: in this sentence, you want to say Number 8, so you need to use 号, it means number. 

Your chinese is good, keep going ! ;)

在火车站。

- 你好。我要买两张车票到北京，五月一号星期日，14：05点，火车的号码G1234。
- 请给我你们的护照。
- 给你 / 恩。请问多少钱？
- 两百块。
- 好的。火车从哪个月台离开？
- 第八个月台。
- 谢谢。

在火车站。

- 你好。我要买两个车票到北京，星期日1五月，14：05点，火车的号码G1234。

你好，我要买张到北京的车票，5月1号， 14点05分开的G1234
- 请你们的护照。

请把你们的护照给我。
- 给你。
- 两百块。
- 好的。火车在哪个站台？
- 第八个站台。
- 谢谢。