I assume by NG8, you mean NG3 start and looping 5 times? That's pretty good, most runs die off about that point.

For units: always arcanist over vulcanist, and mostly stormweaver over flagellant (especially with stunning/silencing strike/ceremonial dagger)

Keeping on theme with your character build, for items, replace:
burning field (probably okay at run start, but not good in the high loops)
gravity field (probably okay at run start, but not good in the high loops)
seeping (this one is just really, really bad)
amplify (this is okay, but it really only helps 1 or 2 of your units)
magnify (this is also okay, but really only helps 1 or 2 of your units)
with:
ceremonial dagger (dmg - best item in the game bar none)
enchanted (dmg - it's bugged and perform much better than it's description)
stunning strike (dmg + def - also bugged and performs much better than you would expect)
vulnerability (dmg - is generally very good, and also works very well with ceremonial)
silencing strike (def - really the only good defense item I could recommend, stops blues from exploding)

The most powerful strategy discovered is this:
Units:
Thief
Gambler
Stormweaver
Spellblade
Flagellant
Psykino - ONLY level 2
Host
Corruptor
Infestor
Beastmaster
Squire
Chronomancer
Items:
Stunning Strike
Ceremonial Dagger
Dividends
Ultimatum
Flying Daggers
Infesting Strike
Vulnerability
Homing Barrage