Need a bit of help with player modifying stuff

So, I'm working on a new plugin which need's alot of player modifying stuff. So here is a few things that I'm in need of help with:
- Changing player speeds Got this working thank god
- Changing player damage dealt with hands(To another player, but only the sender has an increase)
- Changing the amount of damage a Axe wood do.
That's all, hope to receive some help =]