I own a unit on the second floor. 5 days ago, my tenant apparently left the kitchen sink on and caused flooding.

Document everything and if you can prove harm was caused by their action or inaction; that puts you in a better position to have them respond. 

We're glad you weren't offended by our questions and hope you can find a better PMC.Since selecting the wrong PMC is usually more harmful than selecting a bad tenant, you might want to read our series about “How to Screen a PMC Better than a Tenant”:https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processesWe recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

Golf carts are unique, because they potentially not only harm your guests, but other people in the process. 

There's a party wall agreement in place, and our HOA is very limited—they don’t carry any master insurance policy and only handle trash and some parking enforcement.Here’s my concern:What happens if my tenant accidentally leaves a candle burning and it causes a fire that damages my unit and a few of the neighboring units?

Cause and cure for breaching lease - this may or may not be in the standard lease but essentially this paragraph stipulates what actions or lack thereof could cause a breach and how much time does the beaching party have to "cure" the breach.

Do long term tenants tend to cause more wear and tear than a short term guest? 

Delays haven’t caused major issues for me, but they can complicate planning — especially when onboarding new tenants.

Does Investor A have assets worth the pursuit of a plaintiff's attorney if insurance does not cover the harm? 

Notice it says may be covered.The power failure has to be caused by a covered peril.