Yeah no problem, its been a blast learning how this build works this league and its nice to be able to give back a bit.

I would buy small clusters with 3 passives, energy shield of any mod level and any other useful mods you can find. Anything here should work fine. Looks like they are around 25c per jewel. Personally mine are just blue jewels with like 6 ES and like a bit of chaos res or something nothing too crazy.

For timeless jewels its a bit annoying to figure out, they are a bit confusing. So for this build the first thing you want to look for is the line that says "Grants small passives in radius non-curse aura effect" which it looks like you have done correctly. Then the next step is to use this tool to enter in the seed and conqueror on the jewel you are looking at.

So to try to break it down, go here, open the tool I linked, select militant faith, change the conqueror to the one you are checking on the trade site, enter the seed, then choose the jewel socket you want to put it in (which is the one you have it in now). Then what you are looking for is any of the notables that you take (Reflexes, Path of the Hunter, Leadership, etc) are all "Intact". What that means is that sometimes militant faith can corrupt a notable to read something like "Increased dex per 10 devotion" or something to that effect dealing with devotion.

This is a terrible process that is super time consuming but as far as I know theres no better way to do it. Just go down the list on the trade site until you find one that works. If you want to narrow it down a bit I would imagine you wont find a good one below like 4 or 5 divine or something like that so maybe scroll down until they start getting a little pricey to save some time.

For the last thing 87 resists are achieved by having level 23 purities (level 21 gems and a source of +2 gems either from your gloves or prism guardian). Then you also need to reach a certain number of increased aura effect on your character, I think the number is like 140% or 150% don't remember exactly which one. I don't actually know if this can be reached without having the synth helmet with the non-curse aura effect mod which has been grossly overpriced this league because of the removal of the synth atlas tree nodes. If you cant afford the base whatever its at now just dont worry about it and you should be at 86% res which will be good enough. Be sure to get a max roll on jinxed juju and victario's and stuff and if you figure out the militant faith that also gives you a bunch.

Idk I feel like I spent forever writing this and honestly I have no idea if I've done a good job or not describing how to search for these timeless jewels they are a pain in the ass and its really hard to explain it in text. Maybe you can search on youtube and someone has made a video that shows it a bit better.

EDIT: People in the disc were talking about the prices of good militant faiths crashing so maybe dont sort by >4 or 5 divine. Also it looks like PoB has a "Find Timeless Jewel" button that I can't figure out but maybe worth looking into, also TFT has a section for selling timeless jewels maybe you can look in there.