Requirements for IELTS Writing Tasks (Academic). How strict and true are they?

Hello,
I have learned many suggestions on how to write essays from many great teachers, including on this website. However, sometimes the suggestions are opposite to one another and leave me a bit confused. I would like to ask students and teachers here to share their thoughts on the most common advice for writing essays.

The most important question - Where are the requirements listed?

Task 1 (chart graph diagram)
1. Where the "overview" part should be located - at the beginning, at the end or it does not matter?
I have seen essays with an overview in both parts but can not find any rules about it.

2. Is it necessary to include measurement units (like $ billion, kilometres, etc.) in the overview or the paraphrasing sentence?
Some teachers ask for it, some do not. But the test gives only one chance to make it right.

Task 2 (essay)

1. Is it necessary to include a "general statement sentence" in the introduction?
General statement here means that it generalises the topic for the reader convenience but is not mentioned in the prompt question at all. And the second and third sentences where the actual prompt paraphrasing occurs.

2. Some websites suggest explaining your position in the introduction with "This essay will discuss...why I agree/disagree".
Is it a good or a bad idea?

I ask everyone not to look at this as a critique, I do not mean to offend anyone but to clarify some issues I have with understanding IELTS writing. I am willing to follow anyrules that will help me to get an acceptable band score.

I usually put the "overview" at the beginning because it helps everyone easily imagine the task before reading the body instead of putting this at the end. The number of people used the overview above higher than below. But actually, both ways are correct.

Hello..
As I learned before, many teachers suggest me to directly state our idea in the introduction paragraph for writing task 2. This is a good idea, rather than write it just like this "This essay will examine this disputable question and provide possible alternatives". State the idea properly would help us to get higher score because our introduction paragraph is like an abstract, which help the reader to simply understand the full essay before they read all of it.

Hello, RomanKoch,
I have some suggestions for your questions
Task 1:
1) The overview paragraph should be located at the beginning
2) In my opinion, in overview paragraph, there should not be measurement units
Task 2
1) It's up to you, but a general statement sentence can make your essay clear about the context
2) It depends on the topic