If you don't use any other software sources except Play Store and your device isn't rooted then you're secure enough without any additional software.
Indeed, and this is why it is impetative to wait a while after an app is initially released for the Google editors to analyze it for suspicious behavior, and generally only download apps with a high download countPlay store has has had a little bit of a history with having malware infected apps though.
though you should also be careful about your browsing habits as well.
That is probably my biggest worry, is there actually working adblockers for Android? There was none to my knowledge on iOS. There is always pop-up ads when you browse the web on Android in my experience.