Personally, the first thing I do when I get a new system is format and do a clean install. That way I know every program that is installed. But that's me. If you don't want to do that then uninstall any apps you don't want or need.
There are a lot of good AV's - pick a name you've heard of (other than McAfee) and you'll be fine. My personal choice is Kaspersky, but as I said, there are a bunch of good ones. If you want something that's free go with Avira, Avast, AVG or something similar. You should also install MalwareBytes and/or Super AntiSpyware and scan with either or both once every couple of weeks. I also suggest SpywareBlaster. You'll need to update the definitions weekly and it does NOT need to remain "resident".
Last, I strongly recommend the use of Disk Imaging software on a regular basis. Create an image now, before you make any changes. Then you can create images once a week or so and keep the 2 or 3 most recent images. Put the images on a 2nd HD (internal or external).