I purchased glass hole drilling bits on ebay. They aren't the best quality, but will work for more than I need. Remember to DRILL SLOW with lots of liquid to cool the bit.
The sump needs to be large enough to hold the regular water level in the sump plus the extra water from the tank when the pump is off and the water drains down. I would suggest a 20 gallon for a 30/40 gallon tank only because anything smaller would not hold the drainoff.
Take a long time to plan your sump and get good bulkheads and it will payoff later.