Cash out Refi to buy new properties question

[Monte Blunk]

My wife and I are (44 & 49 yo) have been looking into increasing our rental portfolio using the BRRRR method to help fund our retirement and hopefully help to gain financial independence from her W2 job. Over the years we have been taking the Dave Ramsey approach to try to pay everything off. UNTIL we read Rich Dad Poor Dad and started listening to the podcasts on bigger pockets and reading the forums. Here is a little bit about our situation-

We own 2 duplexes and 1 vacation/airbnb rental.  The duplexes both have + cash flow and once paid off could give us around $60K a year in cash flow.  Right now we have over $800/month from each duplex in cash flow.  The vacation rental doesn't currently cash flow more than $100/month but we are hoping for equity in appreciation since it is in a prime ski town.  One of the duplexes has around 250K of equity and the vacation rental has around 150K of equity.  Our primary home has around $500K of equity in it at this time.   We just purchased the 2nd duplex and are currently rehabbing one side to increase the equity in it.    We have been looking at options and are having a hard time figuring out which way to move forward.   

Should we cash out the first duplex at 70% so it would be around $150K and then put that into our own home so we have then take out a HELOC on our home which we think would allow us around $350-450K in funds to use from the HELOC depending on the amount of LTV ratio we can get.

IT seems like a good idea but I am a little nervous about the variability of HELOC's rates and wonder if it is just better to take out the $150K from the rental and then keep it in cash or something more liquid to use to buy properties with traditional loans and then have a lower amount in a HELOC from our primary home. What would be the advantage of putting the 150K in the HELOC that we would then have to pay interest on if we use it?

Any thoughts or advice from those with experience in the area would be greatly appreciated.