Bikepacking counsel - I'm searching for advice on several things, some of them of a more technical nature but given the use case for this build and history of posts I've seen in this sub, I thought it better to post here vs r/bikewrench.

Background: I recently nabbed a Kona Unit X frame in size L that I'll be building into a bikepacking rig with the secondary functions of basic single track and gravel rides with extra thick tires. I've done a lot of traditional bike touring and have been primarily a road cyclist for much of my life. The last few years of owning a gravel bike that I can stick fatter tires on has given me a decent amount of bike packing experience too and I'm reaching what I've theorized is the logical conclusion of anyone who gets into cycle touring: a rigid fork MTB with fat tires that you can put a whole bunch of stuff on and eff off into the wilderness : )

I've built up several road and city bikes in my time and do most of my own maintenance so I'm not totally clueless, but I've never owned a modern MTB and some of the standards I'm wholly inexperienced with. This will be a 1x12 build with a mix of XT and SLX parts as I find them over the next few months.

That leads to my questions:

1. The Unit X if ordered as a complete bike comes with i30 rims and 29" x 2.6" tires. I was planning on doing the same for my build but realized that if anything i'll in the future put thicker tires on it (my gravel bike can already handle 2.1" with style) like 2.8" or even 3.0" so I should probably find i35 or even i40 rims to accomodate. There doesn't seem to be too many of these rims/ wheels around though so I'm keen to hear what your experience with bikepacking on 29" x 2.6" is like and models of suitable rims and wheels.
2. With these builds I buy as much as I can used or source from my parts bin. One thing I may buy new is the crank (I already have a DM chainring) The one thing that has me puzzled is the chainline. I don't understand the difference between the three 1x XT cranks that Shimano offers 8100, 8120 and 8130 or more specifically which fits my use case here. I plan to use 110 x 15 and 148 x 12 wheels. Kona for some stupid reason doesn't have a manual for this bike anywhere I can find so I don't know what the right chainline is.

Thanks for any help!