Hey! Welcome to AN
I definitely wouldn't leave making your summary book to the end of the year as it can take hours and hours to put together and this period of time is when you really want to be doing practice questions and exams.
Using your book for class notes and work could be a good idea, as you will have all of the content that you need to look back on if you get stuck, but it can very easily get messy and confusing (especially if theres a question that you want to refer back to, and you only have the answer - unless you wrote down the question too which adds heaps of time and I definitely don't recommend!).
You could use the loose leaf paper that you said you were going to use and compile it into a big summary book at the end of the year, which is definitely more open to changes, and (check with your teacher for sure) staple and tape the pages together before SAC's as I believe that they consider this as bound. This way, you will have motivation to keep it up to date, because I personally know that I would just leave it till the exam even if I had the best intentions to update it all the time
. You can, of course, remove the tape and staples to add or remove pages that you think is/isn't required. In my opinion, it's better to use the same bound reference throughout the year as you do in the exam (obviously adding to it as you go) as you get a good idea of where everything is.
Totally up to you, though, and what you see is best. You of course can try out different methods throughout the year (e.g. for the first SAC, bring in the class notes and the next the stapled loose leaf paper that you will use as your final summary for the second).