Best time to start ranked

So I have about more that 500 games, joined since 6.10-13ish. I dont have all the champs, but I have the ones I enjoy the most and play well. I main Mid/ADC(Thresh supp and GP top/mid), so usually I get fed unless either: the enemy champ counters me, get camped, or the match is skill and the laner outplays me because of experience. I know all the items in the game and which ill need which in certain match-ups. I am thinking about going ranked and start getting some challenge to improve my skills(I like getting fed, makes me happy), but I dont know when is the time to start doing ranked. I dont have all the champs yet, so the question is, when is it a good time?

My mains(I own the champs, and I play them well): Le mid lane: Le ADC: Le Support: Le Top:

Champions I want to get: SHURIMA , DRAGON BORN , CRAZY , Seen him op wanna try some of that, EVOLVE , LE 3 SHOTS , BLACK(also cool) , BALLS , TENTACLES , GOSU , GLORIOUS REVOLUTION , ANTI-SHURIMA .