PHYSICALLY VISIT YOUR COUNTY "REGISTER OF DEEDS" OFFICE:  That's what they call it in TN. 

The leases I had includes the option, no time limit, and no specific purchase price.So somewhere along the line, the tenant notifies you he will exercise his option to buy.As to why, plenty of reasons.

I know most banks are FDIC insured, but who knows how that whole process would go if it becomes necessary.Therefore, when these guys are saying they have cash ready, do they mean actual physical US dollars, cash in banks (like most Americans), or some other form of asset?

Just notify them, per the terms of the lease of course (ours is 30 days notice on month-to-month contracts), that you are exercising your option to terminate the lease. 

At the end of the term they exercise their option agreement, execute an agreement of purchase, get approved for a mortgage and take title of the property.Make sure you work with an experienced mortgage broker and lawyer to make sure you do things right for your area. 

Then I had the thought that if we just went with simple keypads (programmed only on site, we keep the backup physical key), we could require/help each tenant set their own code at move in.  

Physically look at the software they use and ask them how they are screening, verifying when properties are ready for the investor and how they communicate.Once youre good with that and you’ve got one under your belt, then let todays technology help you make more purchases...

Also, what do people recommend for the physical letters?

Any ideas that don't require my physical presence?

I typically send the video to the prospective tenant and have them fill out an application prior to a physical showing.