I have been an English teacher for 20 years and you actually shouldn't write a conclusion in a language analysis. There is no need to summarise your arguments in a concluding paragraph as you are simply analysing the article written.
In terms of whether you should write an intro, some teachers say yes and others say no. I think if you have time then you should as it is a nice way to open. However your body paragraphs are far more important so if you need to skip the intro in order to ace the body paragraphs, then do so!
It depends on the article. If it is a long article and you have a lot you want to analyse then opt for 4 paagaphs but if it is shorter you may only be able to do 3. There is no right or wrong way to do it :)