How did you derive your maintenance/cap ex estimates?.

You provide some information from which a few numbers can be derived but we need your full PITI after you refi to offer any sound advice. 

We are retired, and the rents are how we derive income.

Remember, on average, the costs will be 50% or so, thus, this should be ammended to say that you will pay no more than "X" Cap of the NOI where the NOI is derived by taking the gross and dividing by 2.

I got one message from their staff appraiser that said "the ADU’s value will be market derived; therefore, value per square foot of an ADU may differ from value per square foot of main dwelling area in a market area."

Either extensively research small unit count maintenance/cap ex costs or derive a detailed spreadsheet of cap ex items to get an idea of the associated costs.I suspect it is more likely that the owning route will cost you an addition $1K/month than that it will save you $1K month. 

Less work than Venmo since Venmo, being a Paypal derivative apparently, maintains a separate balance.

Then there's the market cycle and continuum "timing..." which 'insiders' like the founder (former Saloman vice chairman, and co- developer of the same "mortgage backed securities" derivatives that caused much of the "robo- signed, toxic debt" baked into the  2007- 12 cake, now worth around $2 billion with his 80 page LO 'agreement') would likely have been capable of "doing the numbers on?"

$100/door is trash.Anyone viewing the actual deal metric on the insignificant cash flow it derives is missing the forest for the trees.

I don't get all chummy, we aren't "friends" but I do get to know enough about them that I derive a lot of personal satisfaction from what I provide for them.