Both Chakra Nature and Chakra Reserves matter(Reserves being the amount of chakra the user can call on before he dies.) This is shown with Kakashi, he has been shown with the ability to use, Raiton (Lightning Release), Doton (Earth Release), Suiton (Water Release), and in the anime Katon (Fire Release), but he cannot use Fuuton (Wind Release) as he can't produce the chakra needed to use it. As for Chakra Reserves simply if the Ninja doesn't have enough chakra to complete the jutsu basically he can't use it unless he wants to risk dying and possibly messing up the tech.
In the Narutobase rp we have it set up so that each person can learn all the elements. Thus in the rp sharingan can copy any jutsu it sees except that of a Kekki Genkai. I never seen this actually done I've seen jutsu copied but not copied without prior training in that jutsu.