I've actually ridden in Florida on numerous roads built very similarly to the stretch of US 192 you're concerned about, in addition to thousands of miles of sometimes very busy highway and even interstates. (You may find this strange, but I considered the interstate nearly the safest riding I've ever done.)
From the saddle it looks a whole lot like this. Note that I deliberately pull into the grass to take pictures like this.
US 1 in Bunnell, FL
US 1 in Mims, FL
It doesn't look like it on Google Street View but the shoulder here (and as far as I can tell on US 192) is 4' wide and my touring bike fit fairly comfortably within it with traffic passing by in the right lane. From long experience I'm also accustomed to and comfortable with high speed traffic right next to me. I even look forward to getting a big boost from a passing truck...
The absolute #1 thing I would not want to live without on a road ride is a rear view mirror. Knowing what's going on behind me and being able to see a potential problem coming gives me a lot more confidence on such roads - or any roads, for that matter. Many times I have seen a car drifting over the white line and correcting themselves before they reached me, but one time they didn't move over early enough and I did run off into the grass to avoid them.
I'm a bit shocked that you don't already have a rear view mirror, they are that useful. I can't imagine cycling without it, and sometimes I even miss it when I'm walking around a grocery store or something.
Overall your US 192 doesn't really concern me. For a multilane divided highway the shoulder is adequate and the traffic level appears low enough that pretty much anyone passing you can move over or change lanes entirely. You can even see, in some of the places where Google inexplicably routes around a small town, that the shoulder turns into a bike lane. I would ride it without hesitation. Which brings me to my final recommendation.
I think the second thing you need, after a rear view mirror, is experience. Drivers are well trained to stay in their lanes on such roads, and are very unlikely to be a particular threat to you if you aren't in a travel lane. (Which I've also had to do in various places and that is scary.) But you need to experience it for yourself to really internalize it. Of course I also think you need to experience being able to see what's behind you, and this will also help.
With regard to equipment I just have a plain headlight and taillight, and some additional rear reflectors that came on my panniers. I don't seem to have any issue being seen at night, or at all. I do occasionally wear a hi-vis vest, if I'm on dark unlit roads.
The parts of your trip I find of serious concern are the final few miles, north of Kissimmee, where you are on urban divided highways with no shoulder or bike lane, and traffic is very heavy. In these areas I would not hesitate to use the sidewalk, with extreme caution (this is usually legal outside of central business districts in the US).
Palm Coast Pkwy NE, Palm Coast, FL
In some places you may not be able to avoid riding in the road with no shoulder. You should learn and use the technique of taking the lane in such circumstances. You're legally a vehicle and while you are required to ride as far to the right as is safe, sometimes safety means taking the lane, and others are required to accommodate you when you ride in this way.
It's very rare for a cyclist to be able to take a picture while taking the lane, but I managed it once:
FL-431, Sanford, FL
As you're proposing to do almost a double century ride in one day, I would expect you to arrive later in the evening when the traffic is hopefully lighter. You may wish to pace your ride to try to ensure this.
P.S. Google offered me an alternate route which avoids US 192 almost entirely, and is much more along the back roads. You may find services more limited though.