bicycle seat posts should not give. Your "saddle"/seat should give but most is in tires and hands.

Don't worry about cadence {cranking revolution speed/minute**, but don't hold steady. Vary it a bit, strive for something between 65 and 115. The faster you rotate, the more of the energy is heart, the slower the more it's muscles. Short micro-Sprints are best for developing muscles quickest. Be easy, if it hurts, something is wrong, stop the hurt. Allow time for body to adjust, this is a big change. You'll be working more than the wrists.

Enjoy the trip