Start with BiggerPockets Ultimate Beginners Guide (free).

This is where I would start if I were you—perhaps leveraging one of your existing properties.As a last resort, you could look for a partner willing to fund the project in exchange for a share of the equity.

Quote from @Paul LaValley: I live in Tucson and know Tucson really really well so I want to start here and then jump up to include Phoenix area. 

As for the first investment, I highly recommend starting small, like with a turnkey property or even a 2-4 unit multi-family.

I'm not sure what market you are in but I'm knowledgeable on Columbus Ohio if you ever want to talk about build to rent. it's not purchasing new builds at full market price, it's building it 25% below market yourself 

Traditional lenders won’t approve it, and hard money lenders who offer this type of financing all the time look for experience, assets, or strong equity in the deal.Partnering with someone who has financing or experience is realistic approach when starting.

Join one and start volunteering - it’s the best way to network and meet like minded people.

To determine if an apartment building is a good deal, look at the property's cash flow, cap rate, and potential for rent increases.

They will still do the occasional flip, but mostly when a deal presents itself AND they may be between new construction starts so need to keep their teams busy.

With absolutely no prior experience investing in real estate, I'm getting to the point/age where retirement from corporate America is getting closer and closer, however I still have 2 kids to put through college over ...