Thanks guys for your answers!
@PWM: I'm going to look into aftermarket tankbags first as the Energica one looks massive on the configurator page. If I can't find a suitable one I'll go ahead and buy the official. On my other motorcycle I also use a tankbag for a long time now and I also got rid of the top case that the previous owner has mounted.
@BigPoppa: I didn't like the look of the side case holders when the cases were off, but I'll have a look if I can get something similar to a Kriega in the EU, looks like this will be useful when riding alone.