Ok, im a bit of a noob here myself, but considering how i understand how the arduino works, i would split this into two sections.
first: get the data into the arduino. youve spit into seven "frequencies". For the sake of conversation, lets reduce this to 5.
the arduino takes 5 analogue inputs, so feed each one into each of these.
second: THEN decide what you want to do with the data.
by applying various sketches to each feed, they could do different things.
you could write the data from each feed to a bank of LEDs, as in, "more input" more leds light up (like on an equaliser)
assume you do this for all feeds, you could arrange them in a star shape, so the feeds grow and decrease from the centre of the star, giving different patterns depending on the music (bass heavy would cause it to be weighted to one side or another perhaps?)
or you could influence the colours of some RGB leds based on the frequency?
the arduino could monitor a "beat" based on listening for a pulse (playing with thresholds?) and flash based on a specific beat at a specific frequency?
the possibilities are endless! but yeah, i would split it in two, Get the data in, then worry about what you are going to do with it.
Get some little LEDs going on a bread board, and then by adding transistors or relays, you could replace each output with whatever you wanted (flame throwers would be my suggestion)