The scenario I posted is harsh,but can happen I have a brother who has insurance to cover everything I prefer to just pay for most things.Over time any claims raise the rates to much to suit me.
I don't have any magic number I buy with cash and have 10/25% of purchase price on hand for what ever comes up
I try to have smaller SFRs with fewer tenants less problems.
I figure normal maintenance one to 1 1/2 months rent a year.and plan for a month or two vacant I imagine that is high
my brother figures 3% maintence and 8% vacancy
And keeps and extra 3 months P&I taxes and insurance per property
but I don't know whats the norm
On my first propertys I wasn't really prepared ,after you have a few the losses on one or two won't hurt you much.
The 50% rule covers most things that come up
The age, location or price of a property can change your percentage
I shy away from any POA or HOA and areas with sky high taxes
I am sure you will get better answers from others