@Imran Ahmed If you decide to house hack a duplex using STR, I'd advise getting a property as close to the beach as possible. Being in walking distance from the beach will be one of the greatest impacts on your STR rates. If you can't find a property in walking distance from the beach in your price range, then you need to make sure you can get a property that has an easy route to the beach using a golf cart. (You will need to get a golf cart and bikes for your property if you can't walk to the beach) You can find duplexes at all distances from the beach including beach front. Secondly if you want to take this to the next level of house hacking, I'd STR your unit when you travel. This is just one strategy though; I'm pretty sure you can find a way to make the other house hacking strategies work as well.
I can not speak with respect to St. Augustine and Daytona beach. I'm going to look more into this though. I'd be interested to see how the STR rentals compare to 30a/Walton County.
My project is a spec house in a new development. It involved researching the area for appreciation and what kind of properties were bringing in the most cash on cash return for STR's. My wife and I found a development that was in our price range with a developer that had a good reputation. No homes besides the model were fully completed at the time we signed our contract, but 25% of the development was under contract and currently being built. The developer had an array of homes to chose from, so we chose one that fit our plan, locked in a price, and signed a contract with 5% down to lock in our price. (The developer wanted 10% down with a pre-approval letter, but I negotiated to 5% with a pre-approval letter.) I'm targeting high in guest, but not the highest end guests. DM me if you want more specifics and a link to the neighborhood.