Paragraph size and numbers is arbitrary and depends on your personal style of writing. I prefer depth over breadth and like to interrelate ideas, meaning I tend to have a small number of meaty paragraphs. Others, however, are very good at separating their ideas and arguments, or breaking down their arguments into there base components. Both styles are effective so choose whichever you find easier to write.
Also, some food for thought: you might want to consider planning around arguments rather than paragraphs. A lot of students make plans based on what they are going to write about in each paragraph. I was hopeless at this. I would always have one undeveloped paragraph which I thought would have a lot more content than it did and another paragraph which was 500 words long and still didn't feel 'complete'.
What I ended up doing was just dot pointing 3 or 4 main things I wanted to say and then just paragraphed logically. I felt this gave me a lot of freedom as to what I wrote and how much time I spent on each idea. If I liked where a particular line of thought was going then I could devote 2-3 paragraphs on it and not feel like I was ruining my 'plan'. This meant where there was a particularly meaty idea I wanted to discuss, I could give it the attention it deserved and really attack it in detail. Of course, this did require a bit of on the spot improvisation to make sure everything transitioned nicely but I found it more enjoyable than being limited to a plan that I probably wouldn't follow 30 minutes in. For those who want to try something new, it might be worth writing this way a few times and seeing how you like it.