Conversely, if I choose to retain the three California rentals and pay off their mortgages, my estimated cash flow would be approximately $6,800 per month, albeit with properties that are 20-25 years old.

Common fees will include a set-up fee, a leasing fee for each turnover or a lease renewal fee, marking up maintenance, retaining late fees, and more.

You are not retaining your old property. 

I second the suggestion of retaining a geotech engineer.

The latter seems to provide a middle ground that could enable professional maintenance oversight while allowing me to retain some control, mainly through tenant communication and management portals like RentRedi.

The general rule is at least 1 tub per unit if you want to retain resale value.

Cedar offers natural resistance to rot and pests with a great look that can enhance property value, but at a significantly higher cost and it requires regular maintenance to retain its appearance.

Highly recommend retaining legal counsel to draft a partnership agreement that meets your particular needs.

That is going to cost you $500 / hr with a $5,000 retainer.

If possible a Washer and Dryer, Dishwasher and Microwave, will just make it more convenient and easier to retain your folks if they are longer-term.