Tab key == 4 spaces and auto-indent after curly braces in Vim

Question

How do I make vi-Vim never use tabs (converting spaces to tabs, bad!), makes the tab key == 4 spaces, and automatically indent code after curly brace blocks like Emacs does?

Answer 1

Related, if you open a file that uses both tabs and spaces, assuming you've got

set expandtab ts=4 sw=4 ai

You can replace all the tabs with spaces in the entire file with

:%retab