What other things I need to play a keyboard/synth, except for a keyboard, ofc:)?

It looks as though the EMU longbard would require you to have an amp cable (1/4 inch) to plug into an amplifier. Synthesizers generally need amps unless you buy a toy like a low end yamaha or Casio. Although I think your choice isnt that great, I dont like romplers...it seems like an ok entry level synth. You could also buy usb-midi cables to connect it with your PC for use with DAW programs like Ableton, or Cubase. Midi cables are handy also since you might want to buy a sequencer or effects unit in the future, or control, or slave your keyboard with another synth. Good luck! Hope i helped somewhat.