As a self identified Super Rookie, I would suggest *NOT* rushing in to things. It is good to be excited and motivated, people are here to push you to action. But give yourself the time to learn, strategize, make a plan, and act on it. Especially given today's market conditions. You have time to figure things out.
That being said, @Bonnie Griffin Kaake gave some stellar advice. IMO a HELOC is best used for short term deployments, to get access to quick, short term cash infusions. Like a hard money lender but substantially cheaper for your own acquisitions.
STR is "saturated" everywhere, meaning it is a buzz word everyone is frothing about that surged to the frontlines even when compared to just 2-3 years ago. But what if you spent the time to REALLY understand the STR opportunities in your back yard? Then lazer focus on that, and when you find the right opportunity (location, price tag, income, expenses) you are equipped with your HELOC to take it down. With material participation + cost segregation / bonus depreciation + first year's income, you could be well into paying off that HELOC ASAP (to then go deploy again). For more information on that, check out "Tax Smart Real Estate Investors" on youtube, and find videos tagged with short term rental loophole (many of which can be found in the playlist "The Real Estate CPA Podcast"). You'd ultimately need to connect with a CPA to make sure you are executing this correctly, because there are a lot of steps. But remember, you have time to get your ducks in a row!
Another strategy I have heard people use, is to use a HELOC not for the down payment, but for a full blown cash offer. People were doing this as a way to win bidding wars, but nowadays with price reductions and buyer financing contingency cancellations, you can try to leverage your "sure thing" cash offer to get a discount on the property. Then, after closing, you use delayed financing to immediately turn around and get a long term mortgage to pay off (most) of your HELOC. Check in with lenders to learn more about the practical aspects of doing this.