How many champions and roles should I play in ranked games?

I hope this is in the right section. I don't use the boards very often. Anyway...

I've played LoL casually off and on from season 2-4, and I took a break for most of S5. I almost always play normal games, but lately I've been messing around in ranked. I'd like to get a bit more competitive and serious about the game and work my way up to at least gold. I probably don't play enough (or I'm just not good enough) to get into Plat/Diamond.

EDIT: Follow-up question... Should I just get good with a few of my fav champs or would you recommend taking advantage of certain champs that are currently "over-powered" during a specific patch to climb?

I play all roles EXCEPT top lane. I just never was good at top. I play 6 main supports. 3-5 main ADCs. About 8-10 mid lane champs. And depending on the season/patch/etc, I play about 8-12 junglers.

I always thought that people in higher elos could play at that level with a lot of different champions. Recently I heard that some people just pick 1-2 champions in 1-2 roles (one as a backup), and ONLY play those in ranked.

SO... How many champions and how many roles should I focus on to climb in ranked games?

Thank you in advance :D