I agree with @Rduke77 on two things: that’s not too shabby a roster for a novice. I’ll also say, I learned to raid using a 3-2 way too late. I can’t find the video I watched at that time, but essentially you use three of strong color against the defense’s tank, then two of the strong color against one of the flanks (with the complication that you never want the second color to be weak for either flank) so 3 greens and two yellows against a blue tank or three purples and two reds against a yellow tank (but never 3 greens and two reds). Learning to do this changed everything for me.
Having done one good deed for you (that is, wasting hours of your day finding and watching videos on how to raid), I’ll say that I agree with @Infinite that yellow is a weak spot. Justice is okay, but only as a tank and Telluria is a good tank. I like speed on defense, so I’ll rule out Vivica, too. I’ll also encourage you to start developing troops that accelerate mana, if you haven’t already done so. As in football/soccer, speed kills.
For blue, Vela on a wing. I like Miki for red Titans, but Vela will be on my defense team as soon as I obtain a telescope.
for green, Kingston is good (you’ll love him in raids) but Telluria is your tank.
For purple, I don’t have Kunchen but see him a lot in the diamond arean. I like Sartana, too, especially on the wing.
If yellow is your weak spot, red is your strength. You have some good choices. I like Marjana (more than many who participate in this forum), so I would have her on the wing or flank.
So, my recommendation is: Leonidas - Kunchen - Telluria - Marjana - Vela. (this puts your tank’s weak color next to your tank so as to charge a flank as your opponent tries to take out your tank.)
By the way did you know that you can see how others position their heroes on Titan Mafia? Now I have wasted another hour of your time mulling that over.