If I was starting from scratch, I would buy a duplex/triplex/quadplex, live in the crappiest unit and rent the others out.

The real estate investing industry uses "Classes" to rank property performance risk, but there's NO agreed upon industry model:(Here's what we use for our Metro Detroit market:Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

Start with BiggerPockets Ultimate Beginners Guide (free).

He bought his first couple houses in the first year or two and didn’t buy much for a few years.

If its an investment property and you want to buy out your partner, while you probably have a really good rate - you could get a loan if you have the equity in that property.

The biggest key to a good ROI is getting a good deal when you buy.

I'm a big fan of value-add opportunities, whether it's buying something currently undervalued & fixing it up to my standards, or buying something that has additional income opportunities that have yet to be incorporated. 

I still find this hard to believe. 95% of would be real estate investors never buy a single house.

An investor who is buying the duplex next to mine wants to trade a duplex he owns in a neighborhood nearby so he can have 2 duplexes next to each other (long story no need for those details). 

@Jake Baker  You should think about a rehab loan if you are going to buy and hold.