Hey Kelvin congrats on your free and clear property. I personally like using Helocs for the simple reason that you only pay for what you use. I used one on my primary residence to purchase a duplex.
For a PR most banks don't charge closing costs. On an investment or rental property they will.
TD Bank does Helocs on investment properties. If I remember correctly they offer about 65% of the home's value. They give full details on their website. At one point they were offering 89.99% Helocs on a primary. "SICK"
I can't stress enough how important it is that you do your due diligence when calculating the numbers. Don't leave anything out. Insurance, taxes, cap ex, vacancies, repairs etc.
I would also recommend buying a multifamily. It adds another layer of protection. With a SFR you have to cover all expenses if the tenant stops paying. With a multifamily you will have other tenants contributing.
As a final note you should make sure you can cover all expenses should all tenants stop paying, or interest rates skyrocket in the near future. It's better to be safe then sorry.
Good luck!