Where should I start? Any good companies, or things to look out for? 

I've had a Safeco umbrella policy that covers my primary and 11 rentals for quite some time.

Will an umbrella policy be enough to cover a lawsuit when owning multi family and commercial properties?

Others have two or more properties in each LLC.Umbrella policy + appropriate landlord insurance - A number of our clients combine landlord insurance and an umbrella policy.

You would need to go to a different insurance carrier to get an Umbrella that will only go over your rentals.    

Often it's best to buy in your individual name or living trust and insure well with STR insurance for STR's as well as umbrella coverage of $1M or better. 

Are you able to get umbrella insurance on top of only the rental property?

If your net worth is over $1 million, buy an umbrella policy, you are 10 more likely to be sued personally than your property is.

I understand creating an entity (LLC, etc.) for a flipping business to protect your personal assets from potential issues that arise on a property flip.But my understanding is that if someone gets a judgment against me personally that all of my assets including LLCs are subject to that claim.I already have a $5 million personal umbrella policy.

I mean insurance companies don't write 1 mil umbrellas for 300 a year if they were taking any kind of loss's in the real world..