Mixed-use is a generic term but that typically means there are at least two zoning types for that one lot.  

My plan is to supplement my current career as an auto technician, and to give myself a little extra to retire on.I am pretty good with numbers, and have always managed my personal finances well.

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.

Negotiate the best deal you can with your seller, spell out the terms in the Purchase and sale contract, then fill out the Assignment form for your buyer to sign, and drop the whole bundle off at the title company.The Assignment form I posted is generic and should work in any state.

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.

The rest of it is kinda generic ...

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.