I like it. And all hand built is cool too.
Just a little food for thought. And speaking from a little experience. I think as a end result you would be much happier with the front axle ahead of the steering controls. I know you are still in mock up but I just wanted to share my experience with axle placement in a similar scenario. I have been riding 3 and 4 wheeled ATV's & ATC's for years. Then I built my barstool...... The steering is directly in line with the front wheels, very similar to your front axle placement. It is not a confidence inducing feeling. The 4 wheelers feel right with the wheels out ahead of the steering controls and you. The Barstool was an eye opener as far as stability and feeling "right". I would compare it to feeling like you are steering a unicycle.
Barstool just for reference.
You can see what I mean by the controls being over the axle centerline. Best of luck.
One thing is for sure, it is the most unique!
Doug