Liability insurance question for a rental

[Matt Pastier]

I have my first buy and hold rental in contract and am really excited about it. I got an insurance quote from the same agent that does our primary home and our cars. The quote includes the insurance for the structure, but she is telling me that I will have $300,000 in liability insurance extended from the policy on my primary residence. 

Is it normal to have your liability insurance for a rental property extend from your primary insurance policy? What happens when I have multiple rentals? Lastly, is $300,000 enough? 

I want to make sure I am covered should the worst case scenario happen and I were to get sued for something. Any help and advice would be appreciated!