Do you have a firewall?
The free windows firewall is a good choice
My personal preference is malwarebytes in lieu of your antimalware software, but to answer your question the answer is yes.
You do not want more than one malware product, however. Defender is anti malware.
You may want to look into the free WinPatrol. Scotty, the cute liitle dog, will bark and notify if something new is added to your system. A nice device to have. I know that our own Corrine, recommends the product, too. http://www.winpatrol.com/