英语口语的时态问题When is your vacation going to start?i will be leav

英语口语的时态问题
When is your vacation going to start?
i will be leaving on the fifth of august.1
Oh,that is only a few days from now!How many weeks are you going to be taking?2
I am taking two weeks now,3but i want to save the other week and take it sometime during the winter.
……
what do you like to do?
All the things that you are going to be doing.4
以上这段对话中,多次出现be doing形式.我在很多英语口语中都发现了这类现象,即很多完全可以用do的时候偏偏使用be doing.在语法上虽然都没有错误,但我想知道在地道的英语口语中老外们都偏爱使用be doing的形式吗?
例如,1中,i will leave on the fifth of august即可
2中,how many weeks are you going to take即可
3中,i take two weeks now即可
4中,……that you are going to do即可
希望有一定实力的前辈们来回答,不要说钻牛角尖之类的……