How can I keep my new PC running optimally?

I just purchased a new Dell laptop and received it yesterday. I have been taking precautions to keep it running smoothly: I installed McAffee anti virus software, I have strictly limited my internet access and web surfing, I have no file sharing or instant messaging software, and I plan on purchasing and installing Webroot Spy Sweeper in the next few days.

Here are my questions:

1.) Should I continue to limit my web surfing until I install Spy Sweeper? If so, which sites can I trust? Are Yahoo!, Google, and related big-name sites safer?

2.) Will simply using up storage space on my PC have a significant effect on its speed and efficiency? That is, can I upload music from commercial audio CDs--a safe source--and not worry too much about slowed performance?

3.) What can I do to keep my machine running fast? What should I avoid?

4.) What other precautions should I start or continue to take in order to keep my computer running optimally?

5.) Firefox or Internet Explorer (for security)?

How can I keep my new PC running optimally?anti virus software

1) Anti-virus by itself is not enough. Install the full McAfee Security Suite to get a firewall, Spyware-protection etc. The full suites work better best. If you mix-and-match, the different pieces doesn't recognize or trust each other, and gives you confusing messages. The software in the suites (from McAfee or Norton) prevent bad things from getting into your computer. Some 'Spy Sweeper' just looks for spyware after it has infected your computer, then removes them. It's better to block bad things from ever getting in.