That's wonderful! We haven't been able to find someone willing to give away wood chips. We've tried ChipDrop and others and we're still waiting for a delivery.
I don't have experience with the pellets, sorry! I do know that things like hay, straw, and leaves can mold easily if they get wet. I would think pine shavings wouldn't last very long.
I don't clean out the run. It's best to keep adding things like wood chips on top to let the poop filter down to the bottom. All of it will break down eventually and new bedding can be added on top again. You just don't want to add something that will mold easily.