Getting a license, makes it easier to get access to the MLS which is vital.

Usually a portion of the $700 would go towards interest, taxes, and insurance and the remainder would pay down the balance of the loan just like a traditional mortgage.

You can request a portion of their tax return to verify the rent roll for the duplex, but that seems highly unnecessary.

He offered to let me take this over but he still needs the other $50k equity and didn't seem to be open to the idea of seller financing this portion. 

He desperately wants to sell, but needs a good portion of his equity to pay off debts.  

I will openly state that I plan on retiring early (<45 years old) by using a portion of my retirement accounts (via ladder conversions) to pay off one of my rentals. 

Educating urself is vital!

My management business leases a substantial portion of the property at a market rent.  

I know that in my area, they're a key part of the resale package and provide vital information on the legal formation of the association.

Invest in low cost index funds (like Vanguard total stock market but it depends on what your employer offers)5) Max out your *Roth* IRA for the year ($5.5k) invested the same as above (not point in investing in a traditional IRA given our tax level -- plus you can withdraw Roth IRA contributions in an emergency without a penalty - but you shouldn't as that's what the emergency fund is for)6) Split the rest and invest a portion in the stock market (Vanguard low cost index funds!)