I wouldn't worry. With the smaller ERD of the 650B rim it's really not that extreme. Rears run worse angles than that all the time on the drive-side and the lateral forces on the front wheel are significantly less than the rear. There's no conclusive evidence that 2x vs. 3x has any effect on wheel stiffness on a rim brake front wheel, it's simply trading a small increase in radial load on the hub flanges for a small decrease in weight from shorter spokes. As for tension, once you have enough tension to keep the spokes from unloading, additional tension has no benefit.

tl; dr: Build it the way you would with any other hub and you'll be fine.