Don't depend on Aircover.Homeowners policy will not protect you if your renting as a STR.You need the correct STR policy to protect your property.

I have a mix of long term rentals and STRs and rent some of my STSs mid term in the off season so I am happy to share my thoughts and experiences with each strategy in this area.  

Refinance the whole house as long as the rent exceeds the mortgage?

Still can be very beneficial for a new investor but personally I think not as good as a service as they had with their exclusive listings where they had inspections already done, rent rolls available, and you can complete the entire offer/acceptance via their platform rather than being handed off to an agent. 

I believe I can do this with the upstairs rented out at $1,650 a month and $1,750 for the main floor unit. 3bed 2bath down and 3bed 1bath up.

The best way to think about it is you're in the business of renting a property-that business isn't operational until it's ready and available for rent (aka in service). 

If private companies continue to provide the insurance, I suspect we will see further increased premium costs which will need to be reflected in the rents tenants pay (all tenants: LTR, MTR, STR).  

You cannot rent out an entire home/apartment for fewer than 30 days.Your STR must be registered with the Office of Special Enforcement.

They should be able to determine the COC, annualized return, estimated ARV of a BRRRR, accurate rent comps and more.

I've had them long enough to keep pushing up rents so that I am at the top of my niche, but know not to exceed it because I'm just about at the point where if I raised rents another $50-$100 I'd be crossing over into the lower end for larger units.