To address the concern of the smell of dead mice, I can tell you it eventually goes away. Their carcasses are small and dry out quickly. We lived in a subdivision that was next door to a dairy farm. Every fall when they'd clear it, the mice would come running for the warm, safe haven of our homes. I had traps and poison and would catch several each week, always in the garage or the attic above it. One day, we came home from work and could detect the tell-tale aroma of dead mouse. I checked all my traps and found nothing. The smell got worse for a while, but after about two weeks, the day before my wife had marked on the calendar to just burn the place down, it subsided. Several years later, I discovered why it smelled so bad that time. We remodeled the kitchen and had to remove some sheet rock for a plumbing refit. We found about 30 dead mice carcasses stuffed into a small channel between studs. Apparently, this was the mouse superhighway where they access the garage attic, and a traffic jam backed them all up where they were unable to exit. There was absolutely no smell to the dead ones. The poison I used was they type that makes them very thirsty, so the leave to seek water (assuming you make sure they can;t find it in the house). When they drink, they die.
Now, I am as humane as the next person, but I am not going to jeopardize an investment in my property over the lives of mice. I prefer they do not suffer, but I don't hesitate to kill them if they want to invade my space. We now live in a home that backs up to a nature preserve. We have deer, coyotes, snakes, squirrels, chipmunks, raccoons, and there have even been a few bear sightings int he past. As long as they don't bother me or infest or damage my property, I don't bother them. We do have to be very careful driving in the area as the deer can be very quick to jump out into the road.