From an investment perspective, there's nothing wrong with the stock market but if you invest properly into real estate or even private lending in your retirement account you can get a much higher return than 8%. 

Take ownership of your mistake and learn to do the proper due diligence recommended above😊

It being a headache is only if you can't work with people for properly set up a company with someone.This is what is great about investment partnerships.

Wealthy 2nd homeowners looking for someone to manage their home 11 months out of the year will gladly pay higher fees if you can demonstrate you’ll properly take care of their home and perform well.

(For SF rentals, the odds are surprisingly low if you are managing your business properly.)

But the situation did get me to start thinking on how to properly analyze a small multifamily house.I've only invested in SFRs so I'm a little green when it comes to properly analyzing a duplex.

From personal experience- electric can be very easy, because if wired properly, all circuits should be separate already and connect to one breaker box.

I'm looking mostly for if I buy a 4-unit quadplex (example, or Triplex), how to calculate NOI, Monthly Cash Flow, Rehab, Cap Rate, Cash-on-Cash, etc.For example, whenever I find a property on Crexi, Loopnet, MLS, etc. the NOI sounds good but when you factor in mortgage to get the cash flow, it's almost always negative.I also don't know how to properly calculate a rehab to see ARV so that may be the other issue.

OR you can make money when you buy with properly structured financing.

Once you have a shortlist, sign up for an account with each one and test them extensively to see how they function.