I have recently been interested in these champions, are they good to main for someone not good mechanically?
Top: Garen, Jarvan IV, Darius, Ryze, Swain, Cassiopeia
Jungle: Kindred, Jarvan IV, Sejuani
Mid: Annie, Lulu, Karthus, Cassiopeia, Swain, Brand, Ryze
ADC: Vayne, Jinx, Ashe, Tristana
Support: Nami, Janna, Annie, Soraka, Bard
thats a pretty solid champion pool you got there if you can learn how to play these champions. [slayer-pantheon-thumbs]
Looks good, but I have a few recommendations.
Firstly, it would be a good idea to have an AP jungler as well as an Assassin jungler you're good at.
Maybe a melee support? Someone like Leona or Braum. Always good to be able to play a tank support. Also, a pull support like Thresh, Blitz, or Naut would be useful.
An AD mid would be advisable as well. Zed, Yasuo, etc.
Every champ is viable at low elo. If you want to see win rates for high elo check out champion.gg.
In order to play Cass well you need to be familiar with smart cast so I'd get used to playing with that on (if you haven't yet.)
Karthus and Brand are all about hitting your skill shots so if you struggle with mechanics they may not be the Champs for you.
Vayne is very mechanically difficult. You can certainly play her at low elo but she isn't great unless you have good mechanics.
Don't worry about being good mechanically. If you main a champion, you will improve your mechanics just from playing.
I recommend also learning an AD mid (Talon), a tank support (Braum) and an AP carry jungler (Diana).
as far as support goes just play 
She is unstoppable atm.
First off OP, that's quite a lot of champions to "main." Usually when people say main, they mean the one champ they play and enjoy the most.
Second, if you start playing a champion regularly, they'll get better just by virtue of you being better. I'd worry less about the meta and more about what works for you.
Lastly, great to see a Bard player around here! May your dreams be pleasant and your journeys magical.
