Ranked isn't super toxic as in everyone yells at each other, but toxic players are super toxic and can ruin games for you. I once had a Vladimir who DC and returned 8 minutes in. As Support, I was forced to take his place in mid because we were down a mid laner and I started to build AP. He then returns, proceeds to feed mid lane (4 deaths in about 5 minutes), then complains and goes AFK in fountain. You will occasionally encounter stupid people like this or others who do not know they are losing and attempt to fight someone two levels above them that they have died to multiple times and then complains that no one goes to help them when they constantly try to push out.
You will also run into the occasional bad player (not unskilled, but just an @$$hole who wants you to play a certain champion in a certain position because they don't want to play something with sustain or something that offers crowd control and complain about it. This is less likely than encountering one of the types of players from above. One @$$hole with his friend once banned Zyra and Soraka, both support champions I wanted to play because they wanted me to play Braum just because they did not want to play a tank. Funny thing was that the enemy team picked Braum first anyways and if I had Zyra, I could have easily poked both of them out of lane and allow us to win lane.
All the champions you listed can be played in ranked. Quinn roams a lot and can carry if you are good with her. Ashe is very good for poking down the enemy though you do have to be careful. Teemo is just annoying to deal with, forcing everyone to buy vision wards. Him along with Heimerdinger make very annoying top lane champions that can tilt the enemy if you play them well. Soraka is a good support, especially if your ADC plays too aggressively or carelessly. Those heals will reduce the likelihood of being heavily punished. Sejuani is not as good at lower levels, but is a good tank and has a very good wombo combo ultimate. She is much better at late game, but you might have a lot of problems early on in the jungle if your team is not on top of warding or keeping the enemy jungler out of your own jungle.
Tips:
- I recommend that you have at least 3 champions that you can play for each role that you plan to play in ranked, just in case they ban the things you like to play.
- Ward. You are responsible for your own safety regardless of your role. Hope your allies ward once the laning phase is over.
- Practice last hitting and harassing the enemy in lane along with avoiding being harassed in lane if you haven't. You might want to play a warm up Co-Op vs AI or Normal just to make sure your last hitting is on point before playing ranked.
Optional: Learn to play different styles. The more versatile you are, the better it will be for you when you realize your team is missing something. For example, one tank in the top lane (like Maokai), one assassin in the top lane (like Riven), one tank as a support (like Braum), one healer as a support (like Soraka), and one support with insane poke (like Sona or Zyra). There are many games where missing a tank or someone that can heal can make a huge impact on the outcome of the game.
Quinn, 
Ashe, 
Teemo, 
Soraka, or 
Sejuani are decent champs to use in ranked? I basically main them.
