Here is how my currently setup looks like, now I’m on platinium rank with 2000-2200 cups usually. Other heroes I have which may be an option here are:
BLUE: Boril 3^60, Kiril 3^60, Triton 3^60 (enough materials to fully upgrade one of them)
RED: Wilbur 3^60, Colen 3^60, Scarlett 3^60, Gormek 3^60 (enough materials to fully upgrade one of them)
GREEN: Buddy 3^60, Little John 3^60, Skittleskull 3^60, Kashhrek 1^1 (enough materials to fully upgrade one of them)
YELLOW: Chao 4^70 (with 4 emblems), Danzaburo 3^60, Hu Tao 3^60 (enough materials to fully upgrade one of them)
PURPLE: Tirurtus 4^70, Proteus 3^60, Kageburado 2^60
What would you change here and who should I upgrade first?
Thank you in advance for your help, cheers!
Switch the wings with each other; always yellow near purple. Let the rest as it is. Platinum arena is full of noobs who don’t know to fight 2 healers in the middle and most players at this level consider is a hell of defense. Most of them are afraid even of Kasshrek, but this is another story.
Max up Wilbur and use him as tank, kage as flank, Wilbur kage combo pretty much one shots any hero, li xiu on the right flank, gandalf at left corner, right corner put whoever you want
switch the Li Xiu—Chao
Chao is fast hero and more damage dealer than Xiu…
Other than; with those heroes nothing you can do i suppose wait for 5 star heroes from TC20 and pulls maybe?
GL
As much as I love my Kage, I wouldn’t have him there at 3.70
For starters he’s not really a wing IMHO, he’s a flank. He needs to fire early on in the fight while enemies have over 50% HP left - on the wing he can be ignored a bit longer, but on the flank he’s trouble.
At 3.70, he doesn’t quite have the menace or the sturdiness to sit flank… So I’d sit him out.
As previously suggested, I’d change the order to bring your dark/holy onto the same flank.
wait for 5 star heroes from TC20 and pulls maybe? 
, great for 4