I've had broody hens wean their chicks anywhere from 3 weeks to 3 months of age. The 3 week olds were in the middle of summer, plenty warm enough for them. I've had chicks 5-1/2 weeks old go through nights a little below freezing (25 F). In South Florida your chicks should be able to handle the temperatures fine. It will not hurt them if you provide some heat for them provided they can get away from the heat if they wish. You do not want them to overheat.
my question is should i put some bedding in top of the dirt?
Good question. I don't but a lot of people do. There are some issues.
You want it to be dry, whether it is dirt or bedding. A wet coop or run can lead to disease if it stays wet very long. If water drains away from it then you usually don't have this problem. Rain will blow in from the side but should drain away. If water drains into the coop or run then you can have big problems. Sometimes bedding can help with this but usually not much. The problem is drainage, not the dirt or bedding surface.
If it is dirt and gets wet then they quickly turn that into mud by walking on it. In that case something to walk on can help with mud control. Mud is not in itself dangerous to them but it can be really messy.
I am also buying a chicken coop to put inside the enclosure but that wont come for 2 weeks. My chicks are almost 5 weeks old.
The coop could be important. You want the chicks to be able to stay dry. If rain is blowing on them from the sides this can chill them and cause health issues.
You may be late enough in the year that this isn't a concern, but you don't want a cold wind blowing on them. By now yours have feathered out. They stay warm by trapping tiny pockets of air in their down and feathers. These tiny air pockets insulate them. If a breeze ruffles their feathers it can allow those air pockets to escape. A warm summer breeze isn't a problem, that will not chill them. But cool and especially cold breezes can be.
Their ability to stay dry and get out of a cool breeze would be my concerns. The run turning to mud or holding water instead of draining would be a concern. The age of you chicks isn't to me.