Hello!

English essay is the only subject in CSS that is quite vague. Other critical subjects, precis and islamic studies, can be prepared and could be passed with assurance.

However, we should focus on soild things that can, definitely, improve our position in essay paper. These things are

1) Understanding the topic and writing what has been asked.
2) Legible writing, consistency in style of writing.
3) Proper articulation of ideas.
4) No to minimum grammar and punctuation mistakes.

Moving forward to your questions,
Thesis statement
In my view it should be in the end of introductory paragraph
Historical background
I believe there is not much need to add historical background in the intro if the essay is not about some historical event. However, a minor touch of historical background, for the sake of starting the essay, is recommended but it should not exceed 2-3 sentences. This will give a generalised start to your essay along with completing the narrative writing requirement that is mentioned on the note of the essay paper.
Ideal lengh
1.5 pages
Essay development plan
Introduction have following things
General statements(2-3 Could be historical background)+Paraphrasing of outline+thesis statement
Pattern of introduction fixed/notfixed
I believe it is not fixed ,but you have to write a well organised introduction that must include proper flow of ideas representing outline and upcoming essay paragraphs.
There is no fix way of checking the essay paper. So, keep practicing the things that have definite positive impact on your essay.

Hope it helps.