In regards the topics you will actually teach you'd need to contact the centre themselves for that specific information. However, the tutors on your course will want to see that you can deliver different kinds of lessons to different ability students. You can expect to teach some grammar points/functions but you'll also be asked to do a receptive skills lesson as well as demonstrating that you can facilitate a productive skills class.

In regards the assignments you have to do, I believe the first two are language awareness related.

Your tutor will give you several lexical chunks e.g. looking forward to , as in I'm looking forward to Christmas. You'll be expected to be able to describe various aspects of the lexis including
- The form
- Pronunciation
- Meaning/use
- How you would contextualize the use for students
- What concept checks you would use
- What problems you would anticipate ss having inc. pron, form, meaning/use

You'll notice that the language awareness tasks aren't centred on a whole grammatical structure e.g. The present simple, because the uses/functions of that one structure alone are many and varied (habitual actions, general facts, state verbs, etc., etc.). Reading any of the many books on English grammar cover to cover will give you a good overview of these stuctures and their various functions but i'm not sure how much it will help you with the CELTA not to mention that reading about grammar isn't the most interesting topic in the world. It's probably good to have one such book to hand during your CELTA course for easy reference.

Just remember that the CELTA is an entrance level qualification and therefore you're not expected to know everything. I'd also say that in regards language awareness, you, as a non-native speaker probably have an advantage over most young (under 35) native speakers as they are unlikely to have explictly studied the language whereas to some extent you did.