In the upper left corner in yellow, you will see the skid steer with 440CT model on it. 

I realize we’d probably want to bring in a real estate attorney, but I’m assuming there are models in place that are probably well-established for such a partnership that I know nothing about.

I've done the "Gator" method many years ago not thinking it'd be shilled as a scalable business model.

Myself I used my own internal funds to prove my model.

I like your model for the start and end dates for your units.

Transitions to different rental models?

I think you can model a decent double digit return but how do you transition to actually pulling money out? 

I would not characterize this as a scam per se.. but it appears to me to be a failed investment model..

That is for you to model and assess.

Also, the whole SubTo model is a bit icky and can often get messy from what I've seen.