I own one of these frames. I can confirm that the frame is full internal routing through the headset and you can run a dropper post with the cable going around the bottom bracket area (I have a 150mm oneup dropper v2 in mine)

The only issue with the frame is that it doesn’t actually come with a 52/52 headset. So I had to source my own with a shortened bearing to make sure there wasn’t any gaps below the top cap.

Other than that I am fairly satisfied with the frame, the build was pretty easy and came in right around 9.8 kg.

Which BXT frame were you looking at?

I had an older version of the version of the MTB 036 and didn’t really have any issues with it. But it is worthwhile to keep in mind that the geometry on BXT frames can be a bit wonky since a lot of them have really long chain stays and the headtube tends to be more on the steeper side (though some will argue this is better for stability).

I also heard that the MTB 056 (hardtail Scott Spark) were having a lot of issues with cracking seat stays. I don’t know if they ever addressed this issue with the updated frame though.

Smallest ones I’ve seen are the pro mini’s from jagwire. Never used the before on a build though.

https://www.wheelandsprocket.com/product/jagwire-pro-mini-indexed-inline-adjusters-330244-1.htm?srsltid=AfmBOopWivnlVGtm5PnzXVI696m-Ajd4O2yo_i68h6DmgljAPCaxJS5l

I actually have one of these forks (or at least it looks the same). I bought it from elita one a few years back on sale. The quality of the fork was half decent. 

My issues where: the post mount for the brake was not compleated flat (needed to be faced), the through axle was super heavy, and the fork had somewhat limited tire clearance (2.3 if I remember).

The 480mm should be fine since the 26mm is supposed to correct for the sag of the fork.

I get confused, is boost 52 or 55 chainline?

Boost is 52mm chainline (3mm offset)

A lot of modern frames that have a UDH have boost and a 55mm chainline (0mm offset).

Wolf tooth has a pretty handy guide to chainlines on their webpage as well (there is a table halfway down the page).
https://www.wolftoothcomponents.com/products/direct-mount-chainrings-for-sram-cranks?srsltid=AfmBOoriLY6NTdsP6xWm-agGHPAyWjNq_bWk_Am9fS1rh3oInzgTIGE2

But honestly from my experience getting the chainline wrong is only really going to cause issues with either chainring clearance (contact with the frame) or higher chain wear (replacing chains more often).

Also just as a word of advice, you may also want to buy a bottom bracket tool to install the cranks or have someone install the cranks for you. I’m not sure what bb you currently have, but the evosid bb that comes in the kit uses the Shimano MTB pattern.

Only frames I can think of off the top of my head is the Carbonda FM1001 (trail 135mm) or FM 1002 (150mm AM). Both of them are pretty good and come with a UDH.

I personally have a 1002, and it’s been pretty good to me. But they are a bit on the more expensive side for an open mold frame (last I heard was around 900 with shipping to US).

There’s a pretty extensive discussion on these frame here.

FM 1001
http://chinertown.com/index.php/topic,3104.0.html

FM 1002
http://chinertown.com/index.php?topic=3107.0

I think that you might have the wrong chainring offset for the current frame.

From my knowledge a 55mm chainline needs a 0mm offset chainring or a couple crankset spacers. So using a 3mm offset chainring might be what is causing your shifting issues and interference with the chain stays.

Wolf tooth has a pretty good article about 55mm offset below.

https://www.wolftoothcomponents.com/pages/how-to-find-the-correct-chainring-for-your-mountain-bike-with-sram-transmission