1. Is it a good idea to write 60 to 80 words for my task 2 introduction?
Personally I wouldn't write that many words for the introduction. The main body paragraphs are much more important, so I would spend more time on those.
2. Which verb tense should I use to describe a film or novel?
We normally use the present simple to describe what happens in a film or novel e.g. "the film is about a man who travels to..."
3. The sentences in your ebook are all quite short. Do I need to write some longer, more complex sentences too?
Yes. I tried to limit the length of sentences in the ebook because I wanted to focus on ideas and vocabulary. However, it's easy to make longer, complex sentences by joining two or three ideas together. Remember that long sentences are not necessarily considered 'difficult'. Good writing tends to involve a mix of long and short sentences.
4. Is it ok to introduce myself when writing a complaint letter (GT task 1)?
Yes, that would be fine.
5. Are the academic and general listening tests different?
No, there are no differences in either the listening or the speaking tests.