<Can i put 8 Ghost shrimps in a 10 gallon tank????>
yes, with room to spare
<also can i feed them GoldFish Flakes?>
yep
<would i need a heater with it too?>
no, they'll do perfectly fine at room temp.
i take it you have a goldfish? if so then eventually it will outgrow your 10g and will likely eat the ghost shrimp if/when it can find them.