No issues so far with the seat.
In regards to removing the rear wheel...you just need to remove the cable end at the hub. The cable terminates into a little round nub - I don't know what else to call it. Use a fine pair of needle nose pliers to get a hold of the nub and pop it out. Take note of how the cable is routed around the hub before you do this.
Once the cable is free, loosen both nuts and carefully remove the rear wheel after you release the brake cable. YOu want to be careful by not bending the chain.
To install do the reverse. Just make sure the chain is not to taught - it should have some play in it. Go to Shimano's website and download the instructions for this hub to get the specifications of how much play.
It pays to have a torque wrench also so you do not under or over tighten the nuts.