Almost done with a new VB-186, but while working on the rear derailleur, I realized that instead of shifter cable housing I used brake cable housing. Anyone done this before? Is it no big deal or should I redo all my cabling?

If you used compressionless housing, you 'll be fine.

bit of a noob question but how do you build/service a wheel without access to the nipples? Thank you

First, cut the thread of an old spoke.

Screw it to a nipple.
Put them in the rim by the valve hole.
Use a magnet to drive them through the spoke hole, and get the spoke bit out.
Squeeze the nipple with your thumb.
Unscrew the spoke bit.
Screw the spoke.

Repeat this between 19 and 31 times per wheel
It is easier than it looks, after a couple of wheels it is very fast.

... I usually puncture the rim tape with a needle first, then push the valve through, so the hole is round, and as small as possible.

This ! I do exactly the same.
Using a torch light from inside through the valve hole, to pierce it right in the center.
Then with the valve core srewed 

Trying to figure out if they'll send them to me left rear right front before buying a set, do these use mineral or dot?

Just ask them, Aliexpress sellers are generally quite responsive

I planned to build for riding more than 100km (70-80% pave road)
What I mean is for relaxed bike, not sporty bike.
with 700 with light tyre and wheels.
Now I am looking for tantan GR044
https://www.aliexpress.com/item/1005004310989115.html?spm=a2g0o.store_pc_groupList.8148356.72.179431ffyVym4Z&pdp_npi=2%40dis%21USD%21US%20%24569.00%21US%20%24426.75%21%21%21%21%21%400b0a050b16540920677201880e8436%2112000028709493658%21sh

that frame can ship to my country.
But I don't know about geometry.

Look at how the stack/reach from the aliexpress geometry picture compares to your current bike(s).
You can check with https://geometrygeeks.bike/ too.
Usually gravel frames are more relaxed, but not always.

From memory, Tantan doesn't have a really good after sales service in case something happen.

It is exciting to see some Chinese brands how they try to be as good as the Shimano, SRAM, Hope, etc.
These took good ideas from many models all in one.
Still 128g heavier than my Piccola's but Wow!

...I have the SidLuxe 42.5 in a M M tune and will send it in to be converted to a H M tune. It needs to be High compression and Medium damping...

I have the same, how did you reach the conclusion it needs to be converted ?
Unless a warranty reason, Isn't it something you can do yourself ?