You don't need to install AV. Just don't click email attachments or download random junk.
And then you're in a place where you don't want to be which is where you don't know if you are infected or not. Imagine having a keylogger on there which isn't doing anything malicious to the sytem just monitoring your keystrokes and you then go to your banking site.
MSE for Windows 7 and previous and the inbuilt ones with Windows 8.1 and Windows 10 are fine. Very low resource and do a good job when matched with common sense.
M.