I started with the idea to buy a trike style like you mention. Only they come in road low to the ground, a more upright higher seating position as seen in the image with the yellow frame, and the granny or grandpa styles.

Trikes like to tip in higher speed turns.
Tadpoles handle turns at speed a little better.

The forks will function like the low recumbent in the images as I have them now.

They do turn with the forks like that, just wider than typical. And, later I may replace the front wheels with BMX wheels or smaller to improve turning.

I think when I fit the actual frame to my needs the front forks will be more like the yellow monotype handcycle. That will allow much tighter turns.

As for the design difference from the handcycles now sold. The hand cranks alone can cost over $1,000.

Whole my totsl build will cost $400 to $500.

Brakes will be V brakes 2 front 2 rear. I will upgrade to disc all four wheels at some point.

As for both hands in more of the rowing position or side by side I only need to freewheel one back until aligned with the other. But, you get a more even power output with the position alternating.

The forks will be treated as a single piece. At the positions of either of the images the suspension is not really used or needed. So I will be taking the forks apart to remove the suspension and weld the two pieces into one.

As for vibration I use an air filled cushion that works perfectly for my manual wheelchair. And, like it the air filled tires do alot of absorbing also.

Down the road I may redesign the seat to have shock absorbers to keep the framing simpler.

Diffenately great tips and information that you shared with me, and 99.9% bring the forks to a more upright as in the image with the yellow bike shows.