You CAN run multiple AV solutions but I recommend only doing that for ones you run Manually and that only helps AFTER you've been infected.
Microsoft Security Essentials is "okay" but not as good as paid solutions. You should do some research. You can often get a much better deal when buying for three years and/or multiple PC's.
It's difficult to find the "best" solution as many different sites disagree and of course there's a big price difference. I use Avast in part because of the price.
I also recommend using NoScript with Firefox, and the Web of Trust plugin to help avoid bad sites.
You can Google for more comprehensive tips.
One final note, if you install Windows 8 on a motherboard that supports UEFI and have UEFI mode enabled in the BIOS then your system will be more secure.