One thing to remember is a recumbent is going to take a bit to get used to. It will feel weird at first. I completely understand what you mean by the riding position on the beach cruiser. Any impact with any bump sends the force right into the sore areas, and might hurt like crazy.
A more laid back position would take the road bumps and spread them out over the entire back, and the back would have full support. If its the balance issue, they make recumbent that have 3 wheels eliminating the balance issue all together. You might need to search for Tadpoles.
Now if its the traffic that is scaring you, that traffic is going to be the same regardless of which bike you are on. If traffic bothered you if it got within 10 feet of you on a recumbent, it likely will bother you within ten feet on anything. The question becomes why did it scare you??
If the fear came from real thought out risks, that's one thing. IF that fear is a result of inexperience, lack of recent experience, lack of knowledge, its likely that its something that can be worked through. Yes there are a lot of old geezers that shouldn't be driving in Fl, but it might surprise you they are out on the roads in high numbers almost everywhere.
Could you get hit? Honestly the answer is yes, but they could hit almost anything. You also are not usually helpless in the picture either. A bike stops so fast, often has places where you can go to avoid being hit a car couldn't go and doing the right things on the road can help greatly. Being predictable, lights on all the time and during the day time flashing for sure, flags on lower to the ground recumbents are just some of the things you can take control over to avoid problems.
I suspect what scared you is a feeling of lack of control over the situation. Things like good mirrors, riding aware, practice with emergency stops, and understanding how cars regardless of the age of the driver don't always look for bikes. We must watch out for them, and in fact you should be doing that in most anything you crawl into or on. Yet you are far from being left to the luck of fate. Take control of the things you can control, and then re evaluate the risks. How safe is safe enough is something we all must face.
What often happens if that someone ride a bike a great deal, they often take that heightened awareness into the car and become better drivers. Others just ride more and don't have a car at all.
There are some roads around me I avoid, and other road I ride with no concern at all even though many people think I am crazy. If starting in a low traffic area is possible its a good idea. IF there is something else that scared you, there is an awful lot of experience here. Someone just might have an idea to reduce the risk of what has you uncomfortable and an idea on how to work through it.