I've yet to reach the end of an Eagle XX1.
With the first generation non Eagle XX1, I used to replace the whole transmission every 9 months.
Although I had to change the cheap Aliexpress ring on my FM936 recently, but the chains and cassette are still fine.

Two things have changed since I'm using Eagle chains on my gravel and MTBs.
I rotate 3 chains on each randomly. And hot wax them all together.
It takes about 2h of distant attention(swapping chains every 10' or so) to make 9 to 12 chains.

I started waxing when Marcin from AbsoluteBlack advised me to use squirt in an email.
And then saw the Australian youtuber hot waxing chains.

I always travel with 3 freshly waxed chains, and a small bottle of UFO drip in case of wet rides.

The nero show hosted a very interesting discussion about the replica frames with Joe from Panda Podium.


Long story short, I wouldn't descend an Alps col full speed like I love, with a replica 

...I've decided on the Carbonda FM936 (L) to be ordered soon.

One thing I really can't get figured out is wheels. I was going to go for DT 240s but the 350s are much cheaper and the only diference that I can find is ~40g on the wheel set so I'm inclined to go that way. Rims are another thing. I want carbon but the price of the usual suspects seems astronomical. I'm looking at Carbonbeam 30mm internal in AM (325g)... I'm 90kg+ so shouldn't go super light.

Did you consider the FM909 ? It has the room for two bottles, 52/52 headset, you can lock manually the shock more easily, and is UDH.
I own both, they ride almost the same but with these differences.
An advice more, take the BSA and not the BB92 model, even if not in stock it is worth the wait.

For the wheels. I never changed bearings in a DT-240 wheelset but had to in 350 ones. The 240 come with stainless bearings.
And I ride in the mud 4-5 months a year.
For the rims, you should have a look at lightbicycle.com 
Prices is one thing but you should consider the service that comes with it for all the years you'll ride with them.

In May, I'll celebrate(hopefully) the 10th year of my first 29er rims I got from them.
That will convert to be my gravel set.

There is a new model of the 80-90g full carbon saddle.
https://www.aliexpress.com/item/1005003923285995.html

The previous available came with a 1.45mm carbon sheet, while this new one is 1.75mm
Probably less prone to cracking than the previous one.

I need a non-Boost fitment for SRAM 3 bolt (0mm offset). What are my options here?

I have a Sigeyi on my MTB. XCadey is another one.
However they continuously increased their prices these last years, and I often see good deals on Quarq ones.

I took this one to have a press when not at home.
https://a.aliexpress.com/_EzXDz0N

It is ok, has everything but the DUB size.

I tried the yellow Swiss stop on my road bike last year. The best right ?

And not that impressed by their cost/braking power, I came back to my beloved pink Elite Cooma:
https://alphabicycling.aliexpress.com/store/group/Elite-Brake-Pads/1513091_10000001152730.html
I put them on all kind of bikes: road, gravel, MTB and e-bike.