Novice investor seeking guidance on purchasing my next income property

[Matt Fitzgerald]

Hi, I'm Matt from Boston.  Just read about BiggerPockets on a Motley Fool article about Real Estate investors going bankrupt. 

I work full time for a technology company, but I want to become a full time real estate investor. I own two properties, each is a 2 family. It all goes well, they're my retirement and kid's college education. I rent out 3 units and live in 4th unit. I'm fortunate to have the buildings carry themselves and I pocket $500/month.

Here's how I did it. After a nearly 3 year search for a property that met my criteria - livable, but needs work, under $500k and in the right neighborhood, I bought my first place in one of Boston's most popular neighborhoods in 2010. It took 3 years because all the professional investors gobble them up multifamily properties and flip them into condos. I then bought the attached building 2011 in a private sale from my neighbor. I took a calculated risk and bought each with only 3.5% down because I needed cash for the rehab, I knew the area was extremely popular, and Boston had the highest rents in history at the time.  After 3 years of sweat equity and paying friends and family I'm fortunate to have $400K in equity.

I'm trying to figure out how to make the decision to buy another property and want to make sure I'm not over-leveraged should a down market arise again. Thank you in advance for any guidance that you might be able to lend.