1. not sure, I had to guess and pray it was big enough, I can measure later
2. I wouldnt see why it would be an issue.
3. you dont know the right amount unless you have a meter to read that stuff, its all guesswork. I posted on here a ways back what size holes my reg cooler has or else its on that link in my siggy. It has the drain plug open, and more of that size holes up on the sides, I have one close to the fan, but a tad off to the side, and I have a bunch of smaller holes. again see the link in my siggy and you can look at the holes I have, I have no issues and at this point hatched out tons of chicks in both of them. Only problem I ever had so far is not having an extra fan back up (my issue right now) and a back up power supply, they do fail as mine were already used. I was smart enough to buy extra wafers should they go, but not the fans lol.