What 11 speed 11-32t cassette would you recommend with ER9? Nothing crazy like DA/Red, I was thinking about trying SLR2 sold by Lexon store or Sunshine

To quote a band I like:

"Father, forgive them
For they know not what they do"

Ordered ER9 from 80's designer store, paid 411€ at the checkout. Even if I get hit with full custom tax it won't be that bad.

True, RD13 was not listed. I asked for the lightest possible build for the best price. Leon suggested this, I asked if he could remove the ceramic bearings and use steel (I'm not a big believer in ceramic), he said that these hubs were made for them, so worst case scenario, I put steel bearings in after they deteroriate. Also carbon spokes are new to me, it'll be a learning experience. I have never had a regular spoke brake or fail. We shall find out together if this was a good decision or not 

It appears the carbon spokes require a special hub. This is what I found on it:
https://www.yuananbike.com/product/carbon-spoke-wheeselt-road-rim-brake-wheelset-45mm-rim-depth-29mm-width-tubeless

There are 2 versions of carbon spokes. The more common spokes require special hub, brands like Elite, Magene, etc use these spokes. Less commonly found carbon spokes can be used woth standard huns, i.e. DT240. Farsports uses both types of spokes for their builds

Do you have a link for the Er9 for 485eur? Thanks

https://a.aliexpress.com/_mMUgGy2.
Once you go to check out it is around 510€, then another ~25€ discount from coins

It will probably be more. There is the 21% VAT, there is import tax and the shipping company will want a nice fee...
Try to find a seller that has shipping with prepaid tax? That's almost always cheaper. I've not ordered big items without prepaid tax since they changed the rules in 2021...

Yes, you should be right - total cost is around 30% in taxes, at least from my experience in ordering stuff back in the past. But checking reviews on Ali, it seems like people are sometimes charged with less money than they should be. I wonder if sellers just declare the value to be under 150€, but let you pay the customs yourself?

Why is the AliExpress search absolutely useless? It never brings up the items I'm looking for instead showcasing which I believe are sponsored items. I find it easier to type whatever I'm looking for in Google while adding the word AliExpress to the search field.

IME it shows results based on your search/browsing history. Try to do the search while using incognito mode on the browser

I would consider the new LCR-017 from Lightcarbon.

https://chinertown.com/index.php/topic,4309.0.html

The geometry of 017 is nowhere close to what OP is looking for

Speaking of batteries, how tall is the LTwoo battery housing? I believe Shimano one is 18cm, wondering if LTwoo is any shorter.

I have received the frame just recently and have it assembled to a nearby shop with ceramic BB, OSWP and wheelset from elite wheels and man, it's very responsive 

Did you have any issues with the front derailleur? I believe it is the same design as some Velobuild frames that can make routing the cable difficult, also it is riveted, which I may not trust personally. Haven't built my frame yet, still have to fix the mistakes of my paintjob