Id go with classic physical cluster arrow build with 6pc marauder, bastion of will, hellfire amulet, yang's bow for that massive RCR(f**k multishot bonus), obvious Bombardier, Reaper's wraps/damage reduce bracers, witching hour and cube: calamity/burst of wrath , hexing pants/pride's fall , CoE/Zodiac/Rakoff's (or RoRG for cold or fire variations allowing use of cindercoat etc.)
The main reason why Marauder has been forgotten is propably because Nata and UE bring so much passive damage reduction just by using your basic cycle, making the sets alot less sensitive to positioning and stressful. As for my experience on rift pushing with Marauder; you dont take damage, because you cant handle it. You must control the rift with your slow turrets and allways force max range, which the build excels at. With hexing pants this is extremely efficient (but you will never avain play like a normal person )
With New items and cube i can imagine a few build variations that really help with hatred control, which is the hardest part of cluster arrow.
I was actually just yesterday testing EP quite extensively and this is correct. Set bonus only triggers from your own EP debuff. On the bright side you will still benefit if multiple rune debuffs are used and Gungdo Gears apply to the debuff but the domino effect will activate from anyones killing blow.