From my understanding the all of your RAM uses power even if it's not being used by the phone. So as long as you got some RAM free it's all good. As for closing chrome, I keep on hitting back until it closes (I don't hit home so it closes within a few presses) but closing the tabs and then hitting back works for me too. Just did it and it didn't show up as running. If anything Android will close apps when/if it needs too.
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