Hole diameter will not effect vacuum or amount of said vacuum. Just be sure the throttle blade operates as it should and the hole isn't at a point that the throttle blade closes right on it. Above the throttle blade is ported vacuum ( you only have vacuum when the throttle blade is open ). Below the throttle blade is full time vacuum ( you only have vacuum when the throttle is blade is closed ). If a smaller hole is preferred, an easy fix is to press a piece of soft lead into the hole, then drill out the lead to the size you want. If it was to ever come loose, the soft lead will go right through the engine with no problems.
So, depending on where the hole was drilled, you may or may not have vacuum at idle, but you will have vacuum while driving no matter what.
You should only see the hole on one side of the throttle blade, if you can see it from top and bottom, then its located wrong.
