I can tell you what works. For models you will need to either get some, make some or proxy till it feels right.
I would go with the following to remove dark elf threats. 1 rocket batteries at least 2. Thanks to the FAQ they will remove the cauldron and rider in one lucky shot or at least beat it up fairly well. Also rockets are cheap, so getting 2 is not hard to do.
2 khans for the frenzy stuff, sure they can restrain from charging you. But they have no choice in running straight forward, 2 khans keeps a crap ton of points out of play for several turns.
3 Blunderbusses, dear god they work well against elves. 30 blunderbusses, one shot at range and one more once charged. If you have removed the cauldron then its just dead wytches.
4I look at your list of toys, you are way too combat heavy. You can not play the game of close combat with one of the best close combat armies. If you wish to fight them, then you must soften them up before you fight.
Lastly for crone hellborne, I hate to suggest it but 6 dice spirit leach, every turn. It is a cheesy answer it is a gamey answer, but there is nothing anyone has that can risk hand to hand with her. She has above average chance to kill Sigmar ascended!!! 10 st 10 attacks with asf. There is little in the game that can handle that and actually expect to live. So magic her to death unless she gets stupid and goes solo for some reason. Then fire everything in your army at her. Last line not even joking fire EVERYTHING at her if she is alone.
If that is the new meta, I would just make a standard castle, drop the K’daii for a dreadquake mortar and a hellcannon, and take blunderbuss for core, as well as hobs with bows. Take a prophet with lore of hashut. Drop magma cannons for deathshrikers and pummel them with large blast templates. And when in range give them a nice serving of lead from the blunders.
I’ve had decent luck with K’daii Fireborn against Elves. They don’t do so well against Witch Elves but against everything else they’re pretty darn great. For Witch Elves you can throw Magma Cannons at them to thin them out.
A few Khans definitely won’t hurt to redirect stuff.
K’daii Destroyers are a great answer to just about everything.
Grimbold, K’daii fireborn formation and unit size? I find it difficult for them to be worth it with 2 atks, 2 wounds, t4, and being movement 6,jump out to me as our absolute worst option at 55pts per.
I generally run mine in units of 7 (4 in the front rank) and rely on the burning body to do the real damage. Rerolls to wound mean they have decent staying power and are all but immune to their missile fire. They won’t blow through a unit but they will grind one out pretty well.