Which cluster jewels to run?
Large Cluster Jewels
On a budget
Get a large cluster jewel with at least Prismatic Heart and Stormrider. These can roll on cold damage or spell damage jewels.
Add any source of at least 1 lightning damage to your spells to trigger Stormrider together with the Elementalist ascendancy node.
Better options
If you get enough skill points you can run more large clusters. Here you'll want to include Blanketed Snow and Sadist.
Add any source of at least 1 fire damage to your spells to trigger Sadist's ignite damage increase.
Medium Cluster Jewels for Flasks
To get enough flasks charges to sustain 2-4 flasks simultaneously some flask duration medium cluster jewels are needed.
You will need at least two of them. Or use the calculator to see where you're at and get whatever is needed accordingly.
On a budget
They should have either Fasting + 25% increased effect of small passives or Fasting + Distilled Perfection and come with 6 passives.
You can craft them yourself easily with a bunch of alterations and regal orbs.
Higher Budget Options
You can opt to get some more expensive jewels with 35% increased effect and 3% flask charges gained on them.
They're cheaper to craft them than to buy them. Take around 2k Alterations and get a ilvl 84 base and spam until you get the mods.
Helpful regex:"3% increased flask charges|35%" for one of the mods"3% i.{21}s" "35% i.{14}t" for both simultaneously
Stop if you got both of them as regalling them might brick the jewel with an +armour mod.
If you got currency to burn you can get or create a fractured base with either of those affixes and spam away until you hit Fasting as a notable for maximum flask stuff.
Medium Cluster Jewels for Damage
Get some projectile damage medium cluster jewels with 4-5 passives.
For notables get any combination of Repeater, Eye to Eye, Shrieking Bolts or Aerodynamics if you want additional pierce.