I'm keeping the rental income liquid as emergency money until I get to a certain level, then I'll transfer it to investments - and I have some easily accessible cash to manage any big issues that come up with the property.My question is - I plan to buy two more similar duplexes next year and repeat the same process.

Everyone is different in this situation based on what they have going on in their life.The vacancies on a single family are hard because it will drop your income to 0 for the period it sits.

I can refer you to my investing group's financial experts (accounting firm / law practice), if you like.Where the issue may be getting confused is that the interest on financing is an operating expense for income property, but the principal portion is booked under debt service, as I understand it.

Yes, the headache will be there, but sounds like you'll have a team and if you can target 8-10 of these deals, you'll have a nice stream of income...

This is the key to me as when I do quit my day job I want to be able to add properties without needing a burst of cash or income.

Calculate your NOI (Net Operating Income).

I have been able to save about $20k and am ready to purchase something that will supplement our monthly income without taking too much time away from our current jobs.

Dual income middle class families can afford quite nice rentals.  

Are they refinanced to help lower his monthly debt to income ratio?

I'm currently looking into real estate investments as I am fascinated by the thought of monthly income through rental properties.To get to know me better: I'm currently 19 years old,  a physics student living in Germany and I just read an article about seller financing.Would it be possible that I start investing in rental property or do I need a real job first/assets?