As a general rule, you get much of your -resistance from the constellations. There are three types of resistance shred:
universal to all damage/group of types x% reduced (multiplicative) and does not stack, only highest value
universal to all damage/group of types -x reduced (additive) which also does not stack, only the highest value gets chosen
-x% (additive again), usually restricted to one or two damage types but it does stack from multiple sources
A little more elaboration, roughly speaking, there are 3 tiers of constellations beginning with T1 in the inner regions which house the weak constellations outwards to the T3 regions which house the most powerful. Special mention to Dying God because it is regarded as universally good for anyone going its way. Extra defence is also very valuable like DA and resists. Another thing worth pointing out, PG is based on weapon damage and can therefore leech life, unlike most spells. I have not played a PB spellbreaker so this is just spit balling assuming you go with piercing and cold damage as your primary damage sources:
https://www.grimtools.com/calc/lV7D8X5Z
This is very bare bones. I chose Manticore over Rhowan's Crown because it affects all damage types while RC only affects elemental damage. Murmur for -x% reduced cold damage. Viper for 20% reduced elemental resistance.
You would have enough points left to get Leviathan which is regarded as one of the weaker T3 constellations, but it is still a T3 constellation. You can also get Assassin's Blade for extra -x% piercing damage in the T1 yellow/order region, right side of the middle Crossroads region. Btw you can hover with the mouse courses on the glossary on the upper left corner over the colour symbols and it will highlight which constellations belong to it. If more life you could go Behemoth for a lot of health and health regen.
There are other ways of course to set it up. You could go red/blue and focus on the chaos and vita damage from the skill going for Revenant and then Dying God which is maybe the strongest offensive constellation in the game but the proc is pretty harsh on your life and requires good life leech and/or regeneration to compensate. In that case you would not benefit much from Arcanist though and would have to use it only for its defensive and support skills and passives.
Edit: There is an off hand, Speaker for the Dead, which would convert all piercing damage into cold damage. In that case going Rhowan's Crown over Manticore would be advisable but I do not know if you have that item.
Edit 2: Harra's set is a good choice for that spell breaker, focusing on PB and Callidor's Tempest. Here with the set and Speaker of the Dead:
https://www.grimtools.com/calc/dVbL7oON
Edit 3: A potential full gear setup:
https://www.grimtools.com/calc/r2Bx5RKZ
Try to get close to 26 in PB and 22 in its mods. You do not have to perfectly reach this in every modification or even the main skill just try to get as close as possible. You can get more NB skills from weapon, belt and relics for example.
If you do not want to rely on luck you can go to Grim Dawn forums and look around the trade forum.