How big is your tank? There are these crabs that are called pom pom crabs and they are really small but if you get a lot of them they can be entertaining... I have never owned them but I want to some day
So, there are several kinds of crabs you could keep, but none in the tank as is.
Freshwater pom pom crabs probably should not be kept with anything that could damage them (so very peaceful nano fish only) or that they could catch. They only get about 1.5 inches. They are pretty delicate and need very clean water.
Then you have semi aquatic crabs, which need a paludarium. With a preference for land (70% of tank needs to be land), they need lots of plants with high humidity and enough very clean water to molt in, as well as a high pH for shell growth.
In the tank as pictured, I would not add any crabs.