A MIDI controller is an interface that allows you to edit and control sounds and data from devices that work with MIDI, like your VST plugins, DAW, etc. MIDI is a digital language used by computers and some electronic instruments to share information with each other. 

 Studio monitors are loudspeakers specifically designed for professional audio production applications, such as recording studios, television studios, radio studios, and home studios, where accurate audio reproduction is crucial.  The monitor is designed to produce relatively flat (linear) phase and frequency responses and exhibits minimal emphasis or de-emphasis of particular frequencies.

Studio microphones are the most important studio kits.  A poor quality mic will lead to frustrating recording sessions. Therefore, investing in the best mic you can afford early is a wise investment.

Studio headphones are built primarily for professional work and have sound signatures best suited to recording or mixing. Of course, for your studio setup, you will also need a computer, DAW, an audio interface, microphones, studio monitors, MIDI controllers, etc.