Worst case, slap on some primer, throw down a rug, and voilà: a "blank canvas for the next homeowner."

For me it’s been running toilets and the water/sewer line that ran underground (i recommend getting insurance for it).

Are there any insurance policies or providers you recommend for this unique use case?

As I mentioned above, the risk of being sued, found guilty, and fined more than your insurance will cover is almost non-existent. 

From what I saw for the most part the big names you typically hear in insurance typically performed well for people. 

Now I have to battle the insurance companies.

I believe solid insurance and a good umbrella policy will suffice.

The very basics would be getting your furniture and shopping list together, keyless entry like Schlage (with backup lockbox with physical key very close as well), looking into insurance, local taxes for STRs, and moreAlot of ways to save time and make it easier to self manage with a property management software like Hospitable and data research like AirDNA.

I just have vacant home insurance along with regular home insurance, but no other professional liability insurance.

@Jinglei ShenThe insurance of $1,400 a year seems pretty high in my opinion.