I can see you have put much thought into your project, but I stand by my points - with some more detail. As someone else noted, your wheels, both front and rear, with be rolling through different arcs when turning. For the front wheels that is even more problematic when the wheel is mounted on a tilted/raked fork so means quite a bit of resistance. For the rear that means that you will have to turn the outside crank much faster than the inside one if you want to drive both. I would also anticipate that normal variation in the terrain each is traveling over would make "pedaling" difficult.

Four wheels and weight over the back wheel means you may find a front wheel not contacting the ground when off-road. As to overall weight, the problem is that you are starting out with over 70lbs before any payload, let alone 4 wheels of resistance.

Finally the problem I see with separate cranks outboard is that you are rotating a fairly small circle and rather close to your body, so likely would be using much less of your shoulder muscles than with a wheelchair, and you don't have the advantage of opposition and being able to use both your shoulder and core muscles as with a hand-driven trike. (I will admit this one is a seat of the pants guess - I could certainly be wrong. ...Now that I think about it, there is an advantage to having them to the side, and that is that you could increase the length of the crank arms to give you more leverage, though the problem of the cranks being too close may preclude that being helpful.