The same goes for an excessive number of small holes, like a single wall with 40 nail holes.

@Trevor McCormick,Is there a specific reason to only look at a single market. 

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

Real estate investing has been a passion of mine for time with my mother also having invested early on where I likely have gotten the love and desire to follow similar foot steps.I have taken last 6 months to educate myself and currently own a single family home as primary residence and would like to expand to multi family properties (2-4 units) for additional stream of income, not to mention potential tax benefits for long-term investing.Based on current living situation, I have a fair amount of equity established in my primary residency along with having enough cash to either pay off house completely or use towards investing in a multi family property.Given that I'm the sole source of income for our household with my wife being the home maker for our two kids under 2, trying to weigh out risks with getting started now or perhaps waiting. 

For rentals, would a single floor or two floors makes sense? 

Single family house renting in Goodyear AZ.

We even (I still can't believe it) had a person stay in one of our units that is about $350 a night, who bought EVERY SINGLE PACKAGE (Romantic, Birthday, Breakfast, and Pizza/Smores Kit) and spent $1000 in packages alone.

That's about what I'll get in the stock market plus I'll be liquid (as opposed to underwater the first couple of years) and it's just push button. 

Bundling both properties in a single study may reduce costs.

I have an outdoor pool that easily have 1k+ people using it every season and I never had single complaint due to the water quality.