I would use contitional visibility based on the chosen chart. Create an enumeration with the options for the dropdown and then you can use this enumeration for the conditional visibilty to show the correct chart.
Regards,
Ronald
[EDIT]
Then use MxModelreflection to retrieve all the attributes and show those in the dropdown. Use a reference selector to connect the chosen attribute. For the graph use a microflow as source and based on the chosen attribute create the graph.