Here's some answers. Can I use metal spikes. Yes, if you desire. They are just as safe and don't cause any additional risk of injury. Metal lasts longer, hits farther but costs more initially.
Wood is traditional and sounds nice when the ball is struck properly.
However they break easily and sting in cool weather. Smaller is better in baseball. The baseball is smaller and hard to dig out of large softball mitts. You catch the ball- the glove doesn't. The first thing you notice when go out on the baseball diamond is the distance between bases.