That sounds like a great plan. If they have any specific portfolio guidance, i'd have a check through of that to see if they have any more specific advice or things they look for.
My general portfolio advice is a combination of examples of iteration/development/design work (often the kind of thing you might do in A level), some drawings from life (e.g. still life, figure drawing, technical drawing) and imaginative work (work that demonstrates combining ideas imaginatively). Some places might request a variety of mediums, and these might be specific to your course i.e. if you're applying for a fashion course they might look for textiles work. In your case they might ask for examples of storyboarding or something similar within their portfolio guidance but i'd look at their course-specific guidance to be sure.
Seems like you have a good grasp on all this already and you have a good plan. Good luck!