The seat was $99.00 at northern tool, it only takes a little modifying to fit and does make a big difference in the ride, the factory seat literally has no spring to it to absorb bumps. You do have to disconnect the safety switch that prevents the starter from working if you are not in the seat...
As far as the cold weather I can not answer that as I live in Southern California and we do not have cold weather. Have you thought about making a cover for the valve when not in use?
I do recommend covering the hydraulic lines behind the bucket, almost every tractor I have seen has them bent from something hitting them, and I can only imagine what it would cost to replace them. And for the front bucket I recommend to remove the center chain hook and place one on each side, this would prevent the stress on the center of the bucket, also weld angle iron like I did to upper lip of the bucket, if you do not have a welder check with a friend. I am sorry to say the bumper set up you have more than likely would not help much, the wood would simply break.
I have had several tractors and really like the
b7800 as it has good power to weight ratio and is more of a basic tractor without smog or fancy electronics (less to go Wrong).. Good Luck