I agree with Bitsy.
Also, you will end up using all those pinks over the life of your snake.
When your snake is getting too big for fuzzies, you can feed it a fuzzy and a pink. If your snake ever regurges, you will need pinks. If you ever get another baby, you will need pinks. If you run out of fuzzies, you can give your snake some pinks.
Humane ways to kill mice? I'd do a search on this forum. There are lots of threads I have read on it. Off the top of my head I know that people grab them by the tail and bang them, use cervical dislocation (grab the body in one hand, head in the other- then pull quickly), and stick them in a bag with baking soda and vinegar (this makes CO2, and if you are only offing 1 mouse it isn't too hard.).
I found a guy locally who gasses and freezes mice. Check your local classifieds and ask other snake people. You might be able to find someone. Plus, he saves me tons of money- only $0.88 for an adult mouse, already frozen and bagged!