Herald and Masque are low scoring depravity. Take heralds on Exalted Chariots. They are the same price as daemon princes for +1 depravity. Also based on the rules for mortal wounds, they are treated as wounds for rules purposes, they should grant depravity if mortal wounds were done on the charge by a chariot. If depravity gets errata'd to be only wounds and not mortal wounds, I think you'll have a better time with DP's as the chariots throw out a bunch of attacks but with no rend. YMMV overall.
Your battleline is exactly what I take in my battleline for pretenders. Also remember, keeper of secrets are 20 points less. You have 140 points leftover. You could take 3 endless spells, not really worth it as your keeper is your only caster.
Overall, your depravity for your own heroes dying is 38. Look for maybe higher wound heroes instead of herald and masque. If MW's cause Depravity, then chariots could be a better bet (though a pain to assemble). Also if this is the case, wounds caused by spells would be a great source of depravity, as a chaos sorc on manticore can cause a fair number of wounds without retaliation. If you leave points for spells, take cogs or geminids. Geminids can outpace your army, with being set up 18" away from caster and move 8" the turn they are set up, allowing you hit your enemy with 2d3 mortal wounds on some squads. If you get double turned, you can throw the geminids around with impunity, hurting your enemy more. If you get priority turn 2, the geminids cannot hurt you unless you manage to get into combat turn 1. Mortal wounds done this way can in no way generate depravity as it is not from a hero, so be careful about not losing depravity, unless the batter is heavily in your favor.