How many past papers would you say is enough in a day? Personally i think 5-8
I think the most important thing is being able to make sure that after doing each past paper, you know where you went wrong in the questions where you got less than full marks. You need to be certain after each past paper that if you were to do it again in say a weeks time you'd get full (or very nearly full) marks
That's too many unless they're short exam papers. You need to take time after each one to consider where you went wrong, consolidate, and then move on - unless you consider you were getting full or nearly full marks in all of them. 5-8 seems like you aren't doing it right or work way too long for it to be healthy. But different things work for different people, so...
There really is no point in doing that many past papers if you aren't gaining anything from it. And you can't gain anything if you aren't giving yourself time to figure where you went wrong, why you got it wrong, and how you can improve.
I think the most important thing is being able to make sure that after doing each past paper, you know where you went wrong in the questions where you got less than full marks. You need to be certain after each past paper that if you were to do it again in say a weeks time you'd get full (or very nearly full) marks
I think I could only do a maximum of three per day, and I'd struggle with that. Why don't you spread them out more so you can keep doing them, rather than rushing through them all at once?