Furry's fat and long bikes

Without a bike to try it on I can't be sure...But I would guess that even non offset, the chain should be at least as far from the tyre as a middle ring/lower gears combo with the 17.5mm offset?

At the hub
I'm guessing the Alfine has something like a 47.5mm chainline. So you're going to need to buy say 6mm to clear a 100mm tyre.

At the BB
The outer chainring is 7mm out fro the center ring. so the chainline there is 54.5mm (with standard BB). Which is enough to clear the 100mm tyre already. But its bloody close.

Thats^ assuming a perfectly flat chainline. Pulling the BB end out will have a good effect, as that closest to the tyres widest point.

Have you considered a DH standard 83mm BB width?
Would give you better Q-factor.
Plus the chainline of a single outer mounted ring is 62mm.

I think 100mm is too out of balance witht the rear end.