Keeping the middle owned is important, you gain Ceruleum at 1/tick, might be faster but it's very important considering they are used to summon warmachines.
I know you can find ceruleum tanks on the ground to gain 10 per pickup and I think killing the automatons gives you 1 a kill. I'm not sure if any others give you ceruleum.
Then you have the 3 Warmachines.
Cruise Chaser can have up to 6 summoned aka no limit. It has the least HP 30k, but it does moderate dmg to players and devestating dmg warmachines as well as move fast so you can be evasive.
Oppressor you can only have 2 summoned at a time, It has 75k HP, it's slow moving but it does insane dmg against the Towers 200k a succesful hit. The attack in question is a placed AoE which has diminishing returns depending how far the target is from the radius. The recast of the ability is 15 seconds.
Brute Justice can only be summoned twice a match and only if a tower goes down, 1 for each tower. It does the most dmg to players and decent dmg to towers at 40k being highest I believe. Brute Justice helps to play the defense and while it can be used for offense it's not something you want to rush into the battlefield unless you are confident you will take out a huge portion of the enemy line.
Last line of defense are two cannons, they guard the stairs and are very important in keeping your main tower safe. You can fire off shots in quick succession so you pretty much want to make your opponent dance the moment you get a lock on their location. There is no need to pause your attacks since there is no cost to using the cannons.
However going back to cost, the 3 Warmachines all cost to use and they also use EP to use abilities which can only be recharged with Ceruleum.
All Warmachines cost 50 Ceruleum to summon, 25 to recharge their EP
Also, the map is very important to pay attention to as is the unique UI during the match. It will indicate not only what warmachine is summoned by the enemy side but the map also shows you the location of all active warmachines.
So if you see a warmachine is active on the UI, you can open your map and discern it's location and intercept it to defend your towers.
Basically what you want to do is have Cruise Chasers play defense for the Oppressor while they slowly make their way to the target.