Even if you have to pay more for the purchase think about the costs of carrying the real estate while waiting for the approvals  (debt service, property taxes, insurance, maintenance for the in-place tenant) and the additonal finance charges associated with originating an acquisiton/bridge loan and then a construciton loan at a later date. 

What this means for you s that there is a good chance that your existing SFH becomes rent controlled when the ADU is placed in service (I would like to see the law clarified on this as this practice goes against the rationale of the 15 year exclusion). the reason this is important is that any rent reduction places your base rent at that point for rent control purposes.  

Unsure where you heard this, as the main program is 30 year fixed for DCSR. 

They are your buyers so they can tell you exactly what their formula is, so you can find deals they wantThe ARV*70%-repairs-fee = wholesale price works great mainly for houses under $250K, for houses above that this formula does not work very well in my experience

Also, if you setup a servicing company to manage the payments (usually like $25-35 a month), they can setup an escrow account for taxes and insurance as well and cut a check to her Trust bank account each month.

Also, there are other exemptions as well that don't require it to be your main residence which likely won't be applicable for you, but they may.

In the Tampa area it is still possible to achieve a 5-10% CoC return (sometimes higher) on a property here if you are hiring full service management. 

In hindsight, it's embarrassing to have wasted so much money on services that only wasted my time, caused unneeded stress and frustration, and resulted in no gain of knowledge.

So get a service that will make sure that there are enough funds to be transferred to paying for the seller's mortgage. 

I’m mainly looking in the South or the Mid-West.