I'd always do either 3 or 4 paragraphs for all three sections in the English exam.
For text response, I'd just break down the prompt into 3 main ideas and then try to get one overarching view of the author from each of these ideas. I'd also go through and pick any quotes that I'm going to use (keywords to save time) so that I don't forget them and basically just organise the evidence I'm going to use. If you do things properly, you'll also be able to write the introduction very quickly (it's just a beefed up, pretty version of your plan in theory) and be able to refer to that when you want to know the general idea of what a paragraph will be about.
When it comes to context, I suppose it depends quite a bit on the text type you choose. While I did an expository essay in the exam, I also did narratives for a SAC/prac SAC at school. Because Section B is so open-ended and you can take an infinite amount of approaches, this is just what works best for you. Personally, I'd choose the part(s) of the text that are most relevant to the prompt, and then use that to fill in holes left by my text with wider world examples. This is a pretty simplified version of what's going on, but helps you break down your essay and not have to stop and think every 5 minutes.
In terms of language analysis, a lot of your planning might occur during reading time. You should always do section C first in exam conditions. As a result, I'd quickly highlight any parts of the text I want to refer to, and then jot down the 3 holistic themes/stakeholders. It's also nice to use a "CCTAP" which allows you to identify the context, contention, tone(s), audience, and purpose of the text(s) to make sure you don't miss anything crucial. It's worth noting that where you get the marks in LA (explaining the intended effect of the language and how it operates) might not necessarily be in your plan. You have to make the links yourself and not expect the examiner to guess for you.