I don't get it. You are designing something that will probably weigh in more than 70 lbs, has excess friction and complexity, as well as some apparently impractical design elements, in the quest of what? Even your design of having separate cranks is flawed, as the ergonomics of turning a small radius with each hand outboard of your body would be very inefficient.
Handcycles are available at under $2000, and I easily found lots of listings for used ones well under $1000. I know you may be on a budget, but the fact that it's now so easy to "build" something in 3D is no guarantee it will be easy or even practical in real life.