Fat Bike

offroad fit is not so critical as you are not locked into one position as you tend to be out of the saddle more and varying posture/stance as you navigate obstacles etc

I agree.

Stem length and head tube angle can be more important though. You need to be able to weight, and unweight the front end easily.

Have you considered a 1 x 10 set-up instead of the alfine?

Not so much for weight saving. But for crisper shifting, a more direct feeling drivetrain, and a modular system.

I set mine up last night. I never bothered dialing it in, as the bike isnt finished. But I was still pleasently surprised by how snappy it was.

Sram TT lever in a paul thumbie mount.
Continuous Gore cabling to the derailuer.
Short cage Sram X0 derailuer.
XTR chain and cassette.

Shifting would be a lot better, and when a bit breaks you just replace that bit.