Yes! You can make this cake a day ahead, but wait to decorate it until just ready to serve. If using fruit, the fruits could leak juice which will streak and make a mess!
The other toppings, whether they are small cookies or candies can also be affected over time if they sit in the buttercream for too long. Cookies could get soft from the moisture of the frosting and other toppings might change in texture as well.
It's best to decorate right before serving to avoid any potential disasters!