1700 miles is a long enough ride, but it isn't a long life span for a bike frame. I agree with the idea that generally your wheels components etc... are more likely to let you down than the frame. The average Walmart suspension bike these days would have cost 4000 15 years ago, and you do have to ask whether there are any little bits and pieces that will fall appart. but if the frame is simple, it should be fine.
Check out Ray Jardine's site for an extreme adventurer who has done long hauls on Walmart bikes as well as full custom bikes.
While I like a lot of racks, even when I am going real light, if you do cut the gear down you can easily get by on the rear rack only, and most bikes can mount one in the back. Again Jardine's site will get you on the light path, on the cheap.