Since this may not come into play until several years from now, is there an accepted standard for establishing a fair future rent price based on market rental rates somehow?

Or can I move forward accepting his notice to vacate? 

It kind of reminds me of that George Carlin saying "They don't want a population capable of critical thinking, they want obedient workers, people just smart enough to run the machines and just dumb enough to passively accept their situation."

I’ve noticed there typically isn’t a deadline, but the entity that owns the property will typically accept a sale once they get an offer that meets their terms, often without warning or notice 

Only a few offers will be accepted.

Sounds like you have some of that next level experience that many of us beginners and those of us in the mainstream way of thinking have never dealt with. 

I also accept checks.

@Joe Villeneuve I recently put an offer for a condo (< 100k) and got accepted - it was all cash offer.

Your attorney will have a better idea as to what is cutomary in your area, generally acceptable for private money.

(Yes, I should've only accepted a cashier's check, I'm also reading that even cashier's check can be forged?)