The place is pretty small, and you can do a full visit in just a couple hours, which would leave the rest of the day free to go to one of the cluster of state parks in the area- Big and Little Talbot Island, Ft George, Amelia Island, etc. Those are mostly beaches and picnic spots with some hiking. There's also the Timucuan National Preserve nearby.
The history of the plantation and the Kingsley family is unusual in their views on slavery (as more of a class system than a color issue), and also since for the beginning of the farm it was part of Spain. Because of this, Florida was unique in its cultural blending, though once it became a state a lot of that changed. Yet even through the Civil War, Florida, while part of the Confederacy, still had major differences with the other southern states.
You enter through the semi-circle of slave quarters- some restored, some not, but they ask you not touch or climb around. All the structures on the plantation were built with an oyster shell cement, and you can see how over the years the cement part has eroded away. This area was also plagued with mosquitoes as it was shady and away from the breezy waterway. Bring repellent!
A small garden plot displays the many plants grown on the plantation- indigo, oranges, cotton, sugar cane, beans. There's also a butterfly garden, and if you're lucky (and quiet) you might spy one of the tortoises that live in burrows around the plot.
Unfortunately the plantation house is off limits as it had a huge termite and beetle problem. The rangers said a federal grant had helped them stop the infestation, now they are waiting for the funds to repair the damage. Hopefully it will be open to the public in a couple more years. Meanwhile you can go inside the kitchen house, though it's pretty sparse. Mostly it has displays of info about the family. Info outside the house and in the visitors center shows the layout and pictures of the home.
The barn is pretty small. There was a ranger inside giving details of how they processed the sugarcane and the slaves' workday.
The house is right up by the water, more for transportation factors than view considerations, though it is rather pretty. Most of the original farmland was reclaimed by forest starting in the late 1800s, so the place appears smaller than it was back in the day.
A nearby visitors center has a bookshop and restrooms, otherwise it's a pretty sparse arrangement overall, but the whole thing is free so I'm not complaining too much. It was definitely worth the drive and time spent there, though when I asked the kids that night what they saw that day, they replied "Shrek 2," which they watched in the van on the way back. So much for education.