1. Yes, wider tires and lower pressures can help. Though you are pretty wide at 38mm, if it is a true 38mm.

2. You can also try a sprung saddle, like the Brooks Flyer saddle or the B67. I have both. Flyer on the drop bar bike and B67 on my upright bike. That helped me more than lowering tire pressure.
They really smooth out the bumps. I am 175 pounds and the Flyer and B67 bounce just enough over the ruts and rough roads. Feels like the road shock/bumps goes out the bottom of the saddle rather than up into my body, like with my unsprung saddle.

3. You may need longer reach brakes if you convert to 650b.

4. You may be lowering your bb by going to 650b, which can lead to pedal strike. The folks at Salsa should be able to answer that question for you about your bb height. Or, call the folks at Rivendell VBike Works and see what they say. They are one of the pioneers of modern day 650b bikes and conversions. They know all about that stuff.