One thing to keep in mind if you are designing for someone in a wheelchair is that some of us have little or no movement of, or at, the hips. For instance, in my case, I now cannot sit straight up - with a ninety degree bend. My back is always leaning back. If I sit at the edge of the bed, with my legs off hte bed, I will fall backwards. The chair I use has a recline in it and I cannot bend forward more than a fraction of an inch.
So, if you are testing your design by sitting in a chair, which I recommend, also test the operation without moving your back. I have full range of motion of my arms, thank God, but I could not bend/lean forward to grab a door or grate or to push something. Everything must be done with the movement of the arm.
Also some of us cannot bend our knees properly. In my case, one knee bends pretty well, where my foot touches the floor and my leg forms almost a ninety degree angle. However, my other knee does not bend as far. Some days my foot will still hit the floor, but still sticking out a bit, as my knee doesn't bend ninety degrees. Some days, that knee will cause the leg to stick out in front and my foot will not touch the ground.
So, having a cart, stand, tall legs, etc. for the smoker will be needed for some of us - and not a solid base, but like an open shelf where I could put my leg through if needed to get closer to the smoker.
Being in this position makes everything - every daily thing - so much more difficult...and many things are now impossible. A properly made smoker would open the world of outdoor cooking back up to me/us.
Another consideration - and it is a major one - is cost. Many, or most, of us cannot work and live on disability. I am thankful that my church had disability insurance, but now my family of four must survive off below poverty level income, as neither my wife nor I can work. It will take a looooong time to save money for an expensive, custom smoker. I don't manufacture anything personally, but the fact that these units will not be mass produced in large quantities leads me to believe that production cost - and therefore selling price - may be prohibitive for many, as I have found it is for us.
I pray that, if you decide to move forward with building these, you will be very successful. If I may be of service by answering questions or providing measurements, or whatever, please don't hesitate to ask. I may not benefit from your work, but I would love to be able to help someone else (re-)enter the world of Thin Blue Smoke
God's blessings!