Sump pump: OK to reduce 1.5" to 3/4"?
I have a sump pump that I use with a garden hose. It works great but has a slightly reduced flow capacity. If that size works for you, use it. My greatest concern would be exposure of the pipe to the cold climate. If it freezes, it will not flow water. The smaller pipe (hose) will put more "head" on the pump but should not cause any harm to your pump. As far as cutting a hole to the outside, why not hire someone or rent a drill that can "core drill" an exact size hole to the outside through almost any wall thickness. It will make for a neat and clean hole with little cleanup needed.