You may add on demand scanners like MBAM and Hitman Pro/Emsisoft Emergency Kit but if you don't want you may put it in USB and use in case of emergency.
So since its a gaming therefore you have really low chance to infect.
For Extensions: Adblock Plus is fine and add HTTPS Everywhere to make website you visit is encrypted as possible.
You should add CCleaner too and enable UAC, to minumum level at least, if you are tired of the whole screen pop-up, still better than not having it enabled at all.