Personally I had separate summary books for both Methods and Specialist. I didn't really think of whether I should combine them because I treated them as completely different subjects since they cover quite distinct areas of mathematics with different types of questions and different traps.
Since you are still doing units 1/2 I don't think it matters too much tbh. It is unlikely and probably not too useful for you to use these summary books for units 3/4. IMO the idea of a summary book is about getting just what you need in the book not a huge book where you could teach yourself the subject from - if you wanted that you could take the textbook in. As you said a 5/6 double sided pages of notes is probably good.
Also, summary notes are really not as useful as one would think. Generally of those people who do really well, they wouldn't even touch their summary book throughout the exam - however, the process of making it can be a good revision tool to go back to the theory of the subject.
Someone else asked this question quite recently and
here is the thread.