I'm wondering what people's best experiences with low flow are, reliability, durability, best brands, savings seen, and if I should avoid the extreme low gpf toilets for water savings (0.6-0.8 gpf).

In the end, people rely on internet for all sorts of things and you want that to be reliable.

Alternatively, if you’re using QuickBooks Online with a plan that includes the "Payments" feature, you can collect rent directly through QuickBooks while staying on top of your bookkeeping

Seller financing: Note for $1,350,000.00  - 7% amortized over 30 years with balloon payment after 7 years, interest only. ( I am trying to get the first year at 6% to stabilize then go to 7% remaining 6 years)Property Condition: Above average.

In those cases where a tenant suffered a minor setback and is back on track, if they are scheduled for a hearing before they're evicted they will often pay before that or when they see the notice on the door, but only if you file relatively soon.It really is good screening and filing quickly and consistently that minimize nasty non-payment issues in just about any kind of market. 

I do not understand your remark as related to the DSCR loan.  2 ADUs are not allowed by f/f conventional financing but is not always enforced.Fortunately if you stay with the current tenant without a refi, by the time you pay principle it is likely the rent will have increased enough to absorb the increase mortgage payment. 

I tried to rent one of these buildings for a developer. it was brand new construction, really well done.One after another is was voucher applicants who had criminal records, you had no idea who was actually going to be living there, some were high out of their mind and/or drunk, average credit score was 500, consistent late payments, eviction records, etc.By some miracle I rented one place out to 2 young girls looking to save some money.

In addition to your down payment, plan for closing costs (around 2-5% of the purchase price) and set aside at least 3-6 months of expenses for repairs, maintenance, and vacancies.

In theory, since we don't have a prepayment penalty, you could borrow the money, complete the rehab and pay off your loan before your first payment was due.

The only real advantage to using an FHA loan is to offer only 3.5% down payment, which in my opinion is barely justified as an advantage.