You can set up the arrangements any way you want.  

Even with Covid, we have had a much higher payment rate than many I've read of, although there has been slippage of dates and a couple I've had to work with, arranging for rental assistance.The issue of carrying can be a complex one - you have to be in fear of your life or defending another at the same risk, or you can be in legal jeopardy.

What would a typical arrangement of the lease option be in a situation like this?

Does anyone have any advice for how we should work a deal / arrange a contract if I am investing for example 100K and my partner is investing 50K?

Some folks are going for DST arrangements.

You can find a way to live free or cheap through a house-hack or AirBnB arrangement in most markets. 

I would then confirm exactly when they plan to be out and arrange to pick up the keys and do a walk-thru on that date.  

I was hoping this was a more common arrangement and there was a known simple way to calculate a persons investments value into a shared property 

., BLK 1.71% platforms such as Fundrise and Roofstock that buy and arrange for the management of rentals on behalf of individuals and builder LGI Homes Inc., LGIH 2.47% which now reports wholesale home sales to bulk buyers in its quarterly results.

Before me there was another guy with the same arrangement.