Yes, they can be exchanged, we do it all the time. We use the present progressive to express a future event. I am going to do it tomorrrow = I am doing it tomorrow. The only catch is that we need to say when. "I am doing it" can become confusing if you don't add "tomorrow". This grammar point is covered in the grammar book. Call me on Skype or QQ and I will send you the book and direct you to the page.

"be going to do" isn't a proper way to say anything. I'm going to assume you mean "going to do" Be doing... I assume you mean as used in this sentence, "What is John going to be doing tomorrow night?" Be doing here is the same as "going to do" You could rewrite the sentence, "What is John going to do tomorrow night?" and it means the same thing.