For night city there are a few common combos used. IE and assassin demon spawn to stun and a multi hitter to kill. Horus, prisoner and possibly DDE, horus to stun, prisoner to disable passive and DDE to stun/ kill. The main goal is to permastun the opponents.
Also play arena/ gauntlet as much as possible to earn IC. Those relics really make a huge difference in the long term.
Dont buy event souls, save the ironite for events such LoL frag events or grinding for resources. Try and save as many sacrifices for sac events to maximize the rewards.
Just give the game some time and you will earn the toons needed to compete.