Well, one good thinG about RAM is that you can always add more, with this APU and the type of games you would play on it i think anything goes since we are not talking high performance here, how about you try? get 1 4GB stick and see, if you can play with that setup then you got what you need, if you think games are slower than need be then add another stick to get Dual channel performance, or get a low end dedicated GPU that would be somewhat better than your APU graphics and comes with its own vRAM.
But maybe telling your estimate budget will help others suggest better component selection than what you have your mind set to, maybe drop the APU and get a cheap dedicated graphics card or so?
The optimal situation is 8GB RAM if you can not afford that then anything goes, personally i would get 4GB in Dual channel, a cheap CPU and a dedicated graphics card, this will give you an overall better performance in gaming as 4GB in total system memory will be more than enough for the medium range games you could play on that system if you have a dedicated GPU.