Our short-term goal is to purchase four properties this year with a longer-term plan to supplement retirement from our primary jobs in ten years.

Due to a project close-out and project start-up both occurring this year, I have a short-term goal to use real estate investing as a way to supplement my income, as there will be a 10 to 12 month gap between my last closing (a.k.a. commission check) at the current project and my first closing at the new project, and a long-term goal of building wealth through REI.I am familiar with the process of buying and selling real estate, and even purchased my first "investment" property back in 2007, so I'm also comfortable with being a landlord.

that provides my primary income with the rentals supplementing, but until they hit taxes for 2 years (I bought them all in November of 2013) then my debt to income remains high.Any recommendations?

Investors rely heavily on appreciation on a SFH to make money and will need to be prepared to supplement their tenants rent to cover costs.

More specifically, I am looking for investment vehicles other than "playing the stocks" in which to generate long-term wealth and an additional supplement to retirement.

It isn't my best lead source by far, but it can be a good supplement.

The cynic in me says that REI is not giving them enough cash flow and they need something else to supplement it...

I'm looking toward retiring from my 9 to 5 job in about 10 years, and want to supplement my 401(k)/IRA and Social Security (if it's still around) income. 

My wife and I started out buying a two-unit apartment house about 7 years ago with a similar goal... buying 1-2 small multifamilies per year to hold and pay off the mortgages to cash flow supplemental income.

Also to retire he needs the income from the rental to supplement his pension.