The amount of furniture and fences you need for this project depends on you. If you want to make a very large playground/park, you'll need a suitable number of fences. However, we recommend not skimping on shrubs and fences, as completely surrounding your park with one will really make it more impressive!
The next step will be to change your park's tiles! We recommend placing the Dark Dirt Path tile, as it suits this theme well. You'll be able to change the floor at any point later, so don't worry too much about this choice.
After paving the ground, start placing your furniture! It's good to have furniture other than playground equipment too, such as a clock and benches, as they'll give it a more realistic feel. Even if you have a limited amount of furniture to work with, try recoloring it with the Furniture Customization feature to add some variety!