Such as? Check that the security software is Windows 8.1 compatible before using, don't use older versions. As others have said, third-party security software doesn't run as smoothly as the built-in Windows Defender counterparts.
What programs will you be using?
If you're concerned about the Modern UI / Metro Apps, you don't have to use them. You can right-click and uninstall them from the Start Screen. You can optionally Boot straight to Desktop, or App list view.
You can still customise the Windows Theme/Desktop with a Theme Patcher, but remember to use Windows 8.1 compatible themes.
For Windows 7, you can check what's included in SP1
here. You should install SP1 for Windows 7, if you wish to receive further updates. As suggested this article posted in 2013,
http://www.digitaltrends.com/computing/windows-7-service-pack-1/
Also if you wish to use the latest versions of IE and help keep Windows updated and secure!