Moving from XBox 360 to Xbox one

[WeAllHaveWings]

ds(12) is saving his pennies to buy an Xbox one so he can start talking so some of his pals that have made the move already. Can anyone help with the following question.

I can see when he signs onto Xbox one his account information including subscription to Xbox Gold Live is transferred. When this happens will he still be able to use his Xbox Gold Live on his Xbox 360?

I am assuming as he's not a serious gamer (Fifa, Minecraft, Planets and Zombies only) a 500GB Xbox one will be sufficient?

Is there anything else I need to know?