Please educate yourself, and not just from an internet forum. 

Advice on Layout/Design: For those who have added ADUs, do you recommend standalone units, garage conversions, or a combination of both?

The PM in my mind has the right to lay out the facts as they exist..

The layouts are easier to work with and manipulate to make the space feel as modern as possible. 

Use this amortization table, from a reputable website:http://www.bankrate.com/calculators/mortgages/amor...Ignore the difference in layout/presentation - what's important is that the ending balance for each month in their table matches mine exactly.

Quote from @Mary Jo Carruthers: I have seen houses where folks did it anyways without the permit but that is really value destroying as it will make it very unlikely to sell for top dollar with that layout. 

Narrow your focus, stop buying properties, and figure out what you actually know really well rather than letting FOMO, spreadsheet calculations on faulty pro formas, and advice of strangers on the internet influence your investment decisions. 

Views, location to attractions and layout of property can make or break you in a good location or not so great location.

Best bet is likely (not absolute - everyone's situation is different) is to look at a national lender or broker that has options in lots of states - its a great development versus 20 odd years ago, with technology, internet, places like this - can have access to many more options than before (local broker or lender thats it)

If he's he only one in the area, you could try to do it yourself by making everything automated (such as e-locks, internet, security, laundry, etc.)