Doubt you will need to go 40h, 36 should be sufficient but go with a butted spoke that is 13g at the elbow. Something like the cliffhanger as mentioned above will help a lot though for true plus size tires you might need to look at the blunt 35. Just pair it to a good hub. Personally if I'm building wheels as an upgrade I will start with an XT hub for MTB/Cross/Gravel; shimano doesn't make "wow" factor hubs but the XT or XTR are top quality and reliable. They are built to a better standard and worth the extra money though at XTR pricing I'd start looking at White Industry perhaps.