Here's what I found from the home inspection report the previous investor had done:1) Plumbing outside seems to be ok2) Inspection says Arch Fault Circuit Interrupters need to be added around the house.

I'm assuming you're just adding circuits to a pre-existing load center.

This isn't a deal-breaker for us, but the uncertainty does give us some pause.

@Steve Salisbury usually 2 100 amp load centers or "sub panels " that's based on the breakers feeding them.

Next your going to have to go to the light fixture and probe around until you find a complete circuit.

Since you'll be living in the property, I believe you'll regret skipping electrical updates, etc, as you'll tend to have breakers trip (especially in kitchens).

Basics of what we do:Electrical Check: Breakers, spot check outlets, check GFCI outlets, turn on/off lights, check smoke/CO detector. 

A few of my clients consider retaining walls deal breakers whenever they are purchasing investments.

Is this a deal breaker?

I didn't know he was still on the seminar circuit.