I'm not sure I'd recommend hiking with a plastic body Nikon. The d300 or d200 may be better choices for their durability and weather sealing.
Most would consider 400mm the minimum focal length for wildlife. Although with a crop sensor a 300mm f4 may suffice.
I would disagree, only on the grounds that the OP listed bear in their list of wildlife they want to photograph. My minimum for Bear/Cougar is 800mm. Since I don't have a great need for 800mm I accomplish that with a 400mm f2.8 and the Canon 2X extender. If a grizzle is filling you viewfinder at anything less than 800mm then you are likely to have your name changed to LUNCH!