Gap setting is dependent upon your mashing system. Ideally, you want the crush to be very fine. But that invites plugging the mash and preventing runoff. For starters, I'd suggest a gap of around 0.04" to 0.045" and see how that works in your system. If the runoff rate is pretty high for you, then reduce the gap over successive batches.
I run 0.036" in my Monster 2.2, but I condition my grain prior to crushing and that leaves my crush with a lot of flour and intact husks. Perfect for high extraction efficiency and wort flow. I use one of that Harbor Freight Low-Speed Drills at the lowest speed that it can stand and I can tell you it takes a lot of power. I'd be surprised if a cordless drill would last in that sort of service.