I recommend keeping apps that you use on a daily basis installed on the computer HD while installing your games and other less used programs on the external HD. Follow Steph3n's guidance using the Control Panel, add/remove programs to uninstall the programs you don't need or intend to reinstall on your external HD first. Restart your computer after you have uninstalled all the programs then start installing to your external HD. Even though you are installing to your external HD there will be a number of files that will be written to the computers HD.

You asked about "best-in-class" do you know which of your computer ports are open and can be exploited? Try the free 'SheildsUp' by Gibson Research Corp. No program is installed on your HD so no need to worry about additional clutter. And no I do not work for nor am I related to GRC.