Help and advice for my build

Hi, I am coming back to poe after about a year break or so. I'm after a bit of advice and assistance with my build, based on the spark skill. I'm not interested in changing up the skill at all. I use vaal spark too for bosses and from time to time.
Remember this POB is based on a few leagues ago, so stuff has probably changed since then. I am playing in Standard btw.
For the most part I am able to run up to t9 - t10.. I can run higher but the damage feels low, and my ES isnt quite where I would like it to be either.

https://pastebin.com/QFAbYtjz

Thanks in advance.

First: Spark's heyday was long ago. You were correct to assume that it would be met with a sceptical reception. Most really strong Elementalist lightning builds from the past few leagues used Arc, often in combination with a unique wand called the Poet's Pen.

Second: Your tree has room for improvements in efficiency. Never buy both of the starting nodes. Skip the small nodes leading up to Arcanist's Dominion and bridge across through Practical Application instead. Make sure you're using LocalIdentity's Path of Building Fork and check out the 'Show Node Power' box at the bottom of the tree view.

Third: Simply choosing the defaults can get you into trouble; in particular, Elemental Focus Support is total sabotage for most builds. Lightning skills work extremely well with critical strikes, Shock, and Power Charges, and you can't take advantage of these with Elemental Focus Support or the Elemental Overload keystone. If you try reworking everything (and I do mean everything) around Assassin's Mark instead of Projectile Weakness you'll have a much better time. If you have money to spend, or another character in the current challenge League, you might be able to acquire some Void Battery wands, which are excellent for this kind of build.

Fourth: Atziri's Splendour isn't worth it as a unique chest, especially not for CI. Typically a CI build will want the Zealot's Oath keystone; without it, that +100 Life on Kill is doing nothing for you. Especially in Standard, where you potentially have access to everything from Synthesized Vaal Regalia to no-longer-accessible fossil mods, you'll be able to obtain much higher ES numbers. The same goes for the belt; Bated Breath is a very strong unique, but Crystal Belts can be even better if they're intelligently crafted with fossils and veiled mods.

Hope that gets you started! These threads usually get no love.

Thanks for your help, as you might have been able to tell this was my first ever build I made entirely on my own.. after playing for about a year.
I chose to go with spark, because I like the way it plays, similarly I like builds that use bows, or a kinetic blast wander. Spark just seemed cheap since it was/is as you say past its heyday.

I feel like I should explain some of my decisions, while I am not defending my choices in anyway, nor do I think they are the best or even right, I think it would help with my learning process.

Most of the gear choices were based on cost, where I hardly had any currency. So the splendor worked out well with the large ES value. I'll have a look at a vaal regalia, I know at the time they were super expensive. I seem to remember trying to either roll one myself or keeping an eye out for a decently priced one.

Point taken on the gems, I will definitely look into what I can replace elemental focus with. I think assassins mark might be the direction to go, but yea I will need to see how to rework things - I think the damage boost will do it a lot of good.

I think I could still stretch to zealots oath, like you say it will improve survival significantly.
I think I have a lot to learn still, and there has been a buttload of new content added to the game to take advantage of, especially in the way of crafting.

If you are able to recommend a different build, not specifically elementalist or even witch, but one that would suit my playstyle (preferably CI es too), I would appreciate it. I would like to try to build it up myself without a guide, and only lean on something like that if I need to.. Just a way to try to learn and also keep things interesting.

Thanks again, for your help. Without people like you it would be a lot harder for me to learn about the game.

cheers

Personally I have a long and not-always-successful history of trying to adapt builds into Occultist, so I know where you're coming from when you say you want to figure things out on your own. What I've learned, though, is that you can get better at rolling your own builds by copying someone else first. For example, when I wanted to try Caustic Arrow with CI as an Occultist (which seems like a great fit since CA is Chaos damage but not poison), I built a Raider for CA first using this guide first. That gave me a sense of direction for the gem setup, as well as experience feeling what the result should be like. Playing pure ES builds feels very different from Armour and Evasion/Dodge builds, and it was really eye-opening to be able to get my first-ever Ranger to 93 in a few weeks. It can feel limiting at first, but many of the better-written guides include lots of general advice, including suggestions for farming currency, understanding the passive tree, and crafting gear.

As for meta skills that resemble Arc, you might like some of the Storm Brand builds for Templar. They're not CI; Templar builds generally depend on a gimmick called Mind Over Matter (which uses your mana as pseudo-ES) but with the Ivory Tower unique chest you can build an extremely powerful Low-Life build, like this one, which is very similar to CI in many ways. Because of how heavily intertwined MoM is with the Templar ascendancies, it's very tricky to use MoM with other characters, but if you find the build to be an agreeable experience you'll be in a good position to try an LL Witch based on another unique chest, Shavronne's Wrappings.

Good luck!