What Google Apps can I disable? I'm using a Kitkat 4.4.4 based phone (Samsung Galaxy S Duos 3)
For the most part I don't use G+ or Maps or most of the Google apps provided.
But I do prefer documents being backed up, so I've refrained from shutting down the google app entirely.

Being a phone of very low ram, it kinda cripples the performance. As far as I understand in Android it's not a good idea to kill apps (so normally I hibernate the stuff I don't use). I prefer having the RAM full with apps I actually use.

I'm not really sure what I should be doing with the Google apps. And I would prefer not voiding my warranty by creating a swap partition (using root)
Generally speaking, any system app you can disable can safely be disabled. Core system apps will have the disable button greyed out. You can see this if you open App info for the Settings app itself.

Go ahead and disable all Google apps you don't want.