Your properties sound like they are in decent shape, I’d be willing to bet you have no issues getting the loan.

Probably not that much.Neither you nor I have a crystal ball to see where the economy is headed and what will cause the next downturn, but I'd be willing to bet that when it does happen, the self reinforcing cycle of job lose you mentioned will happen, because the financial market is made up of humans who make sub optimal decisions with incomplete information. 

Seller financing will probably be your best bet

The CPA you spoke to was right, there are tremendous tax benefits for what the IRS calls "real estate professionals" The basic criteria is twofold: 1) you must engage more that half of your 'working' time in real estate related activities. 2) You must spend at least 750 hours involved in RE.What is considered real estate involvement?

I'll bet 99% would agree with rounding up as a no brainer, effortless way to avoid unintended delays.     

This would be an off market transaction, no local agents involved, but still full due diligence for inspections and appraisal. 10% down, 700 +/- credit scores, and good DTI.What's the feasibility of me loaning her the balance of the loan after downpayment, creating a note, and then once it has a three or six month history of performance selling that note?

I would also check your comps in rent say go back over the last 5 years and I would bet you are seeing over time increases to your rent in your area due to growth?

Don't try to do it without someone who knows how to protect the interests of all involved, usually an attorney. 

Too much money involved not to do due dilligence ;)

I am willing to bet that a house of that size with a Koi pond is in a fairly nice area that’s zoned residential, single-family.