Ranked

So I recently got lvl 30. I was thinking of playing ranked but with the season ending soon I figured it would be pretty stupid to start now. I also thought that I only have 1 mid lane champ, which is where I main, the is lvl 5 mastery. So I was thinking that I need to start grinding the champion mastery with about 5-6 other champs to learn them. So I was thinking that I get a few more champs higher levels then about a week or two before the season ends I play my ten ranked games and get a rank for season six. How many of you agree/ disagree with my opinion and why?