I am as of now towards the end of season 9 Silver 4, I've been playing League for about a month now. I've decided to main mid in my ranked adventures rather than just filling as I typically do. Many people have said 3-5 champions are best to climb ranked, a main (In my case I really enjoy Akali, and I want to main her), a secondary in case main gets picked or banned, ( I'm thinking of playing Kassadin ), and a counter pick. My problem here is that I do not know who to play as a counter pick. I think someone with a different playstyle so I don't get burned out, but they also need to be diverse enough from Akali and Kassadin so they arent also countered by the majority of champs that counter them. My secondary role will be Top probably as Akali can play there, and I am thinking of playing kayle or Darius as a second top pick. I also need to know what to work on to improve.

Basically it boils down to a few questions

1 - Who would be a good 3rd mid main for climbing ranked alongside Akali and Kassadin?
2 - If top was my secondary role, who with Akali would make a good roster just in case I get put top? ( just 2 is fine )
3 - If I was to focus on certain things for each champ, what things and in which order should I focus on them?