10, at this stage of exploration in the current game through which I am semi-methodically progressing. (Ignore that.)
Actually, seeing as leveling up can be done so relatively easily, I never feel the need to use Rare Candy. Instead I think it makes a nice little incentive when trading for rare Pokemon.
I only use them if I'm raising a Pokemon for "Data-Only" use, where I'll never battle with it, I just level up and evolve for the Pokedex Data. Then, I attach one to the Pokemon for GTS Bribe-I mean, Trading.
Whoa bro, better slow down bro, don't wanna be a bro, bro.
I have 0 or ∞ i dunno but i use them if i had one but that is not smart :S you need to save them until the last (amount of rare candys) you pkmn lvl need to go so you`re earned more XP'