You need to talk to your insurance agent about finding the right liability policy and umbrella policy.

But get a personal excess liability policy (ie an umbrella) to be safer.

Use the same format as on Schedule E.I would also not only carry insurance on the rental property but add an "umbrella" policy.

Your insurance that you carry with an umbrella would be good enough.  

Other one built in 1949, Allstate agent initially wrote but when assessor went to see it, he didn't even assess due to property's age and they declined to write the policy.I live in NJ and have 2 more rentals in VA so essentially I have 4 properties (including that 1956 built Baltimore), autos and umbrella (requires all covered properties to be insured with Allstate) all with Allstate so trying to see if anyone has their pre-1950 property with Allstate (which happens to be cheapest overall everytime I try to price shop).If anyone has any other insurance company they can recommend for multi-state situation like me then that will be appreciated.

Regarding an LLC - My take is an umbrella policy will cover your risk for 3 to 5 SFHs. 

But I have an umbrella policy too. 

USAA, who I have umbrella coverage with and love working with, said they may be able to put something like this through their underwriting once I am up for renewal in March but I don't want to wait to fill the property or go without coverage in the meantime.

Or, time spent operating a umbrella business for my art/studio sharing that would qualify for a 51% owner occupancy loan? 

I am not an insurance agent or an attorney but you could call your insurance company and they can let you know your coverage and options.I also carry a personal umbrella insurance policy as added protection just in case.