Post-processing is very important. The shots you posted are very obviously out of camera JPEGs, with over-saturated colors that please the average eye, but make some not-so-nice details pop.
So, first thing is to shoot RAW and carefully develop your shots. In this way, you can choose which colors you want to pop, while dulling down some others. Also, if your exposure is not optimal, it's easier to salvage it from a RAW (which has more light/color information than the JPEG).
I second the 50/1.8 purchase. A prime lens is a very interesting tool to learn, and a wide aperture lens is always useful for a cosplay photographer (both to blur backgrounds, and to shoot in low light conditions).