I think it is really important that you establish a good relationship with an independent insurance broker! 

We work with lots of clients that are high earning professionals and are looking to start investing in real estate and we provide a simple solution that doesn't take away from their main focus of their high earning job.

Detailed financial planning analysis can hone in on the actual number with a high degree of accuracy. 

You have an STR listed on the Airbnb platform.Why not look at the design of highly sucessful STR'S in your area and copy some of the best ideas?

To the OP, if you can house hack in your local area, that would reduce the risk of investing in a far away market. 

We do not raise it to market rents, we keep it at lease 10% below to try and reduce turnover.

another property to the portfolio, and a continued relationship with a live long client

It is a new construction where they will not reduce the price in lieu of broker commission to keep their comps high.

When it comes to the HELOC - I'd reach out to any lenders / institutions you have an existing banking relationship with.

I'd start shopping around for terms and building relationships sooner than later.