@Kwok Wong - just chiming in with a few points based on my own personal experience as an investor.
First, if you have no other options, I don't see a problem using your HELOC if the cash flow from your investment will service your HELOC payment and leave you some cash to spare. But highly recommend you have a plan B for making your HELOC payment if you run into a problem with your investment.
Secondly, perhaps consider partnering with another investor if you find a quality opportunity. If you are able to find a great opportunity and need cash and are willing to partner with somebody, contact me or other BP members. If it is an attractive deal, you can negotiate an ownership stake with no money down for simply being the "deal finder." A small stake in an investment is better than nothing.
Thirdly, a couple thoughts on the opportunity you mentioned. Based on current inflation and rates, if that 5.5% rate is fixed for the 10 years, that rate is quite favorable. Also, over the past 37 years, residential real estate on O'ahu appreciates on average about 5.07%. So seems like the only way the deal could work would be as an "appreciation" play. But even then, once you factor in all of your carrying costs, and if the house sits vacant for a bit . . . if you are patient, you'll find better opportunities.
Lastly, I'm not a property manager but I used to rent a house in Hawaii Kai. That $5300/mo rent for a $1.1M home in Kalama Valley seems high - unless the home is comprised of multiple units.
Take care and contact me anytime if I can be of value.