I put in a few miles every year so I’ll give my perspective as a ks “investor”.
Quite frankly, I would be sceptical of a non-functioning prototype. Especially with a design that is not a part of the norm. Most, but certainly not all, cyclists are conservative with regards to design. We buy into the tradition of the the 2 triangle design that hasn’t changed in over 100 years. We have the pro peleton drive our purchasing decision, which has caused Grant Peterson to go somewhat batshit crazy.
Now you are asking me for $1500-$2000 (?) for a frame that looks good on paper. What happens on the A ride when I hit a pot hole and the new design for the head tube snaps like a twig? What are you going to do for me when I take myself out and the 3 riders behind me?
Granted you only need about 50 sales to cover your nut. That’s a pretty low number. But I think it will be a tough sell without a functioning part that has been thoroughly tested. While it will have a higher long-term capital cost and a higher upfront cost, you could have a mold made of only the medium before you make the other sizes.
If you can, get into contact with Ritte. They are a boutique builder and could have some insight introducing a small run to the public.
Also, since the law has changed to first to file, you should consider a provisional patent sooner rather than later.