You can get simple drill stops for just a couple dollars at your local Home Depot, Menard's or other hardware store. Or, just use a piece of tape as your guide and watch carefully.

Well good thing you blurred out the 50013 and the... 771876?

Does not matter at all, only thing it could do is help you. If your game was stolen you have a record of the serial number. I don't see any benefit in "hiding" a serial.

I wouldn't even both with batteries even remotely mounted. Get nvram

No, the entire point of NVRAM is to save high scores and settings without batteries. They are less than $20 shipped and you just unplug your existing RAM and replace with the NVRAM.

Very nicely done. You could sell these!

Nice font choice! Is that T2 font a regular or custom one?

I think he is getting at the subsurface corrosion, i.e. the dark areas. These have not been neutralized so may corrode away again and cause issues in the future. The board still has value but it takes quite a bit of time to properly neutralize and clean corrosion to prevent it for good.

Don't forget to stick a block of foam behind the skull if you haven't already.