Seriously, dont sweat the offset right now. Find the frame you want and go from there. The last 2-3 forks I built were basically from scratch buying steerers, legs, dampers, and airshafts separately.
It's an easy swap to make if you ever decide to do so. Plus pike steerers are super cheap comparatively.
I've had 100-135mm 29er trailbikes and IMHO, a 120ish mm is the sweet spot for around here. Anything less is tough to get the rear suspension dialed since there's such a small amount of travel, and more just feels like overkill for general use.