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.

While I wouldn't need to make a too much to supplement my retirement income, I definitely like the process of REI, and would like to explore some additional avenues like getting my RE license or possibly look at doing financing.  

You will need a longer history of earning those variable income types if using a degree to supplement your work history.As mentioned above, if you truly want to buy an investment and you won't be living in the home,  investment properties don't qualify for FHA loans.

We BRRRR 8-10 peryear and the flips supplement and money left in the BRRRRs.How do we choosewhich ones to BRRRR?

Building a note investment business that generates monthly cash flow of at least $1K a month within the next 5 years to supplement my expected other sources retirement income is my current goal.