You can't 0% it without cheating. Well, on original difficulty; but I'm almost certain it stands for casual too.
Maaaybe you can do the school door with 0% (the door's boss is gonna be very hard though), the goblin door is defo doable with 0%, the bunny door - not possible, you WILL get at least 3% (get your 5 endurance down to 2 at any rate which translates to corruption too) to be able to save the other girl after some running around; incidentally you need to do this to get the true ending as well), and the monster door... Nah, definitely not possible on the first go (again, at least on original diff). You will need a good -at least!- 2-3 loops to actually stand a chance here. Also, these stats/stat increases are needed for the final boss too, so you will have to grind here.
10-15% is roughly the best you can do if trying very hard and maybe even save-scumming...
Not really a problem, because almost quite literally the only change you will see is the final battle's difficulty against the big boss - and that just gives you a handicap (and QTEs, which could get you a different bad end too though, I think) IF you are on at least 50%... Returning to the main "hall" any time with 100% or more will get you another bad end. But that's it.
So you shouldn't stress over it, really - there's no changes in scenes or some such connected to the corruption (apart from the above mentioned). I was worried too, though, but alas, for nothing... xD