You should write the Task 2 essay first because it is longer and worth 60% of your writing grade.
You should write a minimum of 250 words, but you can write more words as long as they add and expand your ideas. Do not write repetitive ideas or irrelevant ideas.
You should spend about 40 - 45 minutes on this task.
Agree/ Disagree essays usually provide a statement about some issue; then they usually ask to whether you agree or disagree with the statement.
The question usually states:
Statement: The IELTS task 2 essay is very simple to write.
Question: To what extent do you agree or disagree with the statement?
It is more academic and a better strategy to write ideas for both sides.