This all came from NREIG's proposal.They did pay, but it seemed to be unusually cumbersome.

Unusual but possible. 

-I would need to hire a Real Estate Attorney to draft this unusual purchase contract, and that would be an extra cost.

If you’re prepared financially and find a good opportunity now, it might be wise to proceed rather than waiting for uncertain future changes.Ultimately, it’s about balancing predictions with your personal and financial goals.

They will get a "Loan Payoff" from the lender....but it would be very unusual for a lender to ask to see the formal note itself.  

“Force Majeure” means: hurricanes, floods, extreme weather, earthquakes, fires, or other acts of God, unusual transportation delays, wars, insurrections, civil unrest, or acts of terrorism, governmental actions and mandates, government shut downs, epidemics, or pandemics, which, by exercise of reasonable diligent effort, the non-performing party is unable in whole or in part to prevent or overcome.

I self-manage a property in California and have never worked with a PMC before, so I'm uncertain about what my responsibilities are compared to those of the property manager.

Look for evidence of an additional roommate or anything else unusual.

That's not unusual.

Also, they prefer an uncertain big payoff to a certain but lower payoff - even when they on average earn more per hour if they just charge for their time.