For all the work you will be doing and odds and ends to adapt it just look around. I just found like 4 npr trucks that run and drive on marketplace for under 5k. In the long run its gonna definitely be cheaper with a much better outcome. I do totally see how you will get more done with existing parts and $300 at a time but if you save up and spend 4-5k on a chassis that’s already driving and has good power, brakes, axles, complete drivetrain made to just do everything your asking......well you get what i mean when i say you will be ahead.