I want to create process author on case module

Hello ,

I want to create process author for below conditions.

1. when i gets new case that time i want alert to assign user

2. when assign user getting changed that time alert to related assigned user.

3. when my case status goes closed so i want to send alert to related client.

4. if my cases are not closed between 48 hours so i want to send alert to related assign user.

Can anybody give ideas for how to achieve these things.