My HELOC will help supplement financing costs, and rehabs in the event the HM isn't favorable.

The supplemental bill was over $7000! 

Certainly the experience will help....but I would look at PM as more taking a job to be able to make money to supplement buying properties with your wife. 

No, not 1 singular mention of the trillions kicked out to help supplement people, apparently that was National Beer Money day. 

If you run your numbers well, each property should give you a monthly cash flow which you can either use to supplement your own income or use towards the acquisition of additional properties and scale in this manner.

We are close(ish) to retirement -- maybe 5 years -- so our first inclination is a buy and hold strategy with the aim of building cash flow to supplement eventual retirement income as well as equity that would likely be useful 15-20 years down the road.

My parents recently asked me to look into some real estate investment options to supplement their pensions.

That's perfectly fine and fair-- just keep the assets to supplement your life style in the most risk-averse and conductive to living a free life. 

Just like most everyone else, I really enjoy my job and where I am at in my career but I would like to supplement CALPERS with REI, and give my wife the option to not work if she chooses.  

While I wish these courses were available when I was in college, I think at the higher levels they supplement formal education and can’t replace some of it.Practically speaking for example, medical students must still open cadavers and spend time in a hospital, budding chemists and engineers must spend time in a lab, and even welders and machinists must get hand on experience.