Will the internally assessed work take up a lot of my time?

It should do! In the first year of the course (AS) the internally assessed work - a research study on a topic you choose and a book review that you choose - counts for 40% of the marks so you will only do well if you give this work the attention it deserves. This shouldn’t all be in your own private study time, your teacher will almost certainly arrange for some class time to be spent in preparation and completion of these tasks.