mud flaps for the front fender.
lizard skin seal or piece of rubber tube for the lower piece of the headset
avid BB7 is not a bad choice for disc brakes and they are available in both road and mtb lever configurations.
You talking about about wrapping a tube around the lower headset circumferentially or trying to make a seal with the rubber tube somehow? I've heard about doing this but never seen it/tried it. You have any pics?