Firefox is easy to install and works far better than IE. You do need to keep IE available because there are a few (very few) sites that specifically look for IE before allowing downloads.
Nope. But then neither does MicroSoft. They announced over a year ago that they were dropping support for Outlook Express. No more security updates, no new versions.
You can still use Outlook Express and Firefox will inteface with most any mail program you use including those from M$.
Avant is nice. I keep IE, Firefox, Mozilla, Netscape, Maxthon, Avant and Opera on my desktop to use in testing web pages. Of those, I would say Avant is probably my second choice.