It was good exercise for both of us and moved the needle forward.

A lot of long-time agents end up in a similar spot.One thing I’d gently challenge is the idea that the “unicorn” has to come purely from market selection.

This isn’t a rushed upgrade or a box-checking exercise.

That's way too much exercising for me.I dunno, seems a bit risky to hold paper claiming to be a partial interest in a company and not understand what I'm doing. 

Pex is flexible, so you can get it to make gentle bends without joints.Pex typically does not burst even if it freezes.

Single-family tends to teach fundamentals like tenant management, financing, and cash flow discipline, while commercial forces you to think more about income, expenses, and structure.Since you already own a single-family home, even running numbers on it as a rental (realistic rent, expenses, taxes, reserves) can be a great learning exercise before jumping into the next deal.

Fortunately I have never had to exercise plan b.  

• Is it non-refundable consideration for the option itself,• credited/deducted from the future purchase price if the tenant exercises,• or refundable under certain conditions?

The mortgagee has a claim on the title that he can exercise by foreclosure on the mortgage. 

But this is a good thought exercise.