I have had my BBU almost a year now.
To answer your questions, Axiom makes a rear rake that is just for disc brakes, about $30.00, any bike shop that buys from QBP (quality bike parts) can order one for you. It is a nicely made solid rack. I have had 40 lbs plus on it, no problems.
The stock tires and rims really are not suitable for off road riding. I built a second set up with Mavic 719 rims and 38 mm conti top touring tires, softened up the commuting ride, as well. The stock seat post sucks, replace it with a better one, I opted for a X1 suspension post, went with a brook b17 saddle as well.
I am not sure about touring long distances on this bike, I have done 60 miles unloaded on the NCR trail in MD its a rail bed converted to a trail. Longest road ride about the same distance.
I bought the bike for commuting to work, knowing I could get a second wheel set and go off road with it.
To sum it up it is a fine bike but would be reluctant to take it on a long road tour.