1)
man df
man grep
man date
man <whatever shell you use>

That should be all you need... maybe "man sed" and "man awk" too if you're feeling adventurous - there are many ways to solve this.

2)
man cron

Part of the fun of learning UNIX is searching these forums and Google - a voyage of discovery....

People are not going to write your scripts for you. We are all more than willing to help people and answer specific questions - not regurgitate manual pages and write complete solutions.

Cheers
ZB