For an outdoor plant, it is a good idea to make the cut at an angle. Otherwise water pools in the middle of the core bit when it sinks in after callousing and mold and stuff grows in there. Unless you never get damp weather where you're at. For an outdoor plant I doubt that angle vs. flat is going to make a difference when it comes to number or size of pups. It's going to produce whatever it feels like producing either way. Besides, with trichs, more pups = less overall growth on each one. As for treating the exposed cut, I'd simply make the cut early on a day thats forecast to be warm and sunny, then in the evening cover it with something to shield it from moisture, such as a plastic bowl or bucket. Then take that off whenver the sun is out until the thing seems sufficiently calloused.