Most investors have rose-colored-glasses when it comes to their neighborhood quality.

Without accounting for management fees (I have not yet decided if I will try to self manage), and with planning to raise rents to typical market of $825 for each of the smaller units, and $1200 for the larger unit, does this seem like a worthy first investment? 

Get the russet or white potatoes.

Typically 75% of rental income can be applied towards your DTI for qualification. 

Typically the first set of tenants I screen are the ones who end up in the unit due to prescreening activities like my application and making sure I meet them.

Issues 1) even garage conversion ADUs in single family zoned areas typically cost more to build than the value that they add.  

So, a house that would typically cost $100 per sq. ft. to build 5 years ago, is now costing $200 per sq. ft. 

It'll be easier to start with a turn-key property, but if you have a good contracting team, a value add will typically offer better returns. 

typically no special license is needed when doing it for hard money loans that I am aware of. there may be states like california and nevada that are tricky where lenders need a license of some sort but for most part brokers i have seen are not licensed. 14 or 15 states require state license and NMLS registration.

Yes, when there are multiple adult occupants, you would typically combine their gross incomes to determine if they meet the income criteria.