Lots of good info here. One small additional thing is to consider the type and size of baskets you intend to use. If you'll only use solo and doppio baskets, then nearly any size hole saw will do; as all you need do is use one big enough to expose all the tiny holes on the bottom of the basket(s). However, if you plan to use the modified portafilter to pull triple shots, then you need to measure the diameter of the triple basket and be sure it will clear the bottom of the modified portafilter. This is because most portafilters are not deep enough to tale a triple basket. You need to get this right the first time, as once you drill out the bottom with a hole saw, it's not easy to use a size or two up with a hand drill, as you no longer have a centre hole for the hole saw.