The equipment from the planner above has all exalted items plus a Tempest Maw to show the accessibility of this build without needing a bunch of uniques or legendaries as well as good affixes to strive for. However, one great thing about this build is the affix variety, there are a lot of different 'GG' rolls for items. The section below has the same affixes applied as in the build planner, but with additional uniques suggested to look out for with high LP.
For defense, make sure your resistances are capped, you have either 100% crit avoidance or almost 100% reduced damage from crits, then just stack Health and Armor wherever you can. I haven't found the gear to test a low health version of this build yet although I understand those are pretty strong. Considering you don't have good ward options I'm not sure how viable it would be on this build. Regardless, you need to be dodging one-shot mechanics anyway.
For leech, try to find a Bleeding Heart with LP to slam offensive affixes. Since we're not stacking melee damage, melee leech isn't very helpful for us and the sources of spell leech available aren't great. A Bleeding Heart can you get back to full almost immediately while casting Tempest Strike, and I've found that you cap out at like 4-5 stacks of bleed which does negligible (like less than 10) damage. If you can't find one, I recommend using the Black Sun blessing and relic implicit for spell damage leech. If you feel that your leech is strong enough without it, an Eye of Storms amulet with at least 1 LP would be a good replacement.
For offense you have a lot of great affix options; below is a priority list. To my understanding, % bonuses are multiplicative against each other, so it's good to have these as even as possible to maximize damage output. For example, 400% increase to lightning damage and 0% increase to spell damage won't be as strong as a 200% increase to both.
- PrefixSpell Damage - flat sources of spell damage and particularly lightning spell damage will be scaled by multipliers and thus are extremely strong.
- PrefixCritical Strike Multiplier - this stat is harder to get access to, so taking this wherever possible will help bring your crit multiplier in line with your % lightning and % spell damage bonuses.
- PrefixSpell Critical Strike Chance - this affix can roll higher than general critical strike chance and should be prioritized when possible.
- PrefixCritical Strike Chance - prioritize this until your crit chance is as high as possible. Your character sheet won't show storm bolt's actual crit chance since it's getting base from Maelstrom so you'll need to do some calculations making assumptions about how many Maelstrom stacks you're maintaining regularly.
- PrefixLightning Penetration/SuffixLightning Penetration and Minion Lightning Penetration - this is always a priority as a suffix on a weapon, but you'll need to evaluate your other stats and test if this is worth replacing other prefixes on amulets.
- PrefixAttunement - your 'main' stat. Best acquired on armor. On jewelry, exalted PrefixLightning Damage or exalted PrefixSpell Damage may be preferred depending on the rest of your gear.
- PrefixMelee Attack Speed - this will let you expend stacks faster, but you get pretty insane attack speed from Aspect of the Shark, Fury Strikes 3/3, and Windfury 1/1 that the above should be prioritized.
- PrefixLightning Damage - use wherever possible unless the above are available .
- PrefixSpell Damage - same as above.
- PrefixMelee Lightning Damage - we don't scale melee damage, but this will still scale off % lightning damage bonuses, so not a total waste of a slot.
- PrefixStrength - similarly to the above, it will provide a damage boost, but never preferred over Attunement for damage or Vitality for surivivability.
Obviously these options aren't all available on every item so be intuitive about what affixes you choose. That being said, don't be dismayed if your exalted scepter has %spell damage instead of spell crit or multi, one of the good things about this build is that all of these affixes are enjoyed.
The important thing is making sure your covering your bases. Don't take the below affixes as gospel, the gear drops you get will likely determine what affixes you need to craft into across items.
I've also included some ideal uniques below. The only two I'd suggest swapping out immediately even with 0 LP are Tempest Maw and Stormcarved Testament. These are very strong on their own, but not required to make the build function. The rest of these have stats that support the build, but are only worth equipping if you can make a good legendary out of them. You'll have to evaluate what affixes you're giving up to replace exalteds/rares with uniques/legendaries. It's unlikely you'll find any of these with 4 LP, so make sure you're not doing something like leaving yourself at 30% void resistance just to put on Stormhide Paws.