whether you actually need a traditional AV in addition to Appguard depends on your level of paranoia, and also on how you go about installing new programs. When you install new programs, Appguard won't be protecting you, but a traditional AV will protect. So if you don't totally trust what you are installing, i.e., you take risks sometimes, so Avast or Webroot will be a good, very light AV for you. If you go for Avast, choose custom install, and ditch the bloatware.
You could also consider installing an anti-exploit, such as Malwarebytes Anti-Exploit, or HitmanPro.Alert (it is stronger than MBAE, but more prone to conflicts). You will not feel the impact of these programs. They run super light.