What does landlord insurance cover if you're investing in an apartment building with 100 + units?

Also, what's covered by this insurance.

In my area they can rent out at 1,000-1,200 all day long, and since there's so much demand, I can screen tenants properly without having to compromise just to avoid vacancy.

Screen tenants and get the most qualified ones you can and require a large deposit of they don't have good credit and background checks.

Based on what other places are rented for in this area, the rental income will likely cover more than half of our estimated monthly fee (mortgage, property taxes, etc.)I'm wondering if anyone who owns a property in this area has dabbled in AirBnB and what their experience has been like?

I can team up with couple of agents but  Roofstock or HomeUnion are working probably hundreds of agents therefore would cover more markets.

Often times the rent will cover or exceed your mortgage costs.

He is looking to move in with his SigO but is concerned his rent wont cover mortgage/expenses.

The difference being that the buyer's policy does not cover total replacement if the house burns down and it essentially just covers your investment in the house. 

If a claim were to happen while the property is vacant and being renovated/repaired, the insurance company would not cover it if it's insured on a landlord policy.You need to purchase a vacant property policy.