I've given myself 9 months to complete this project
Excellent, we get so many people with such a complex project and they say it has to be ready next week. Given that amount of time you should be able to tackle it.
so I'm splitting the project up into parts
That is the correct approach.
For the lots of LEDs see the port expander on this project:-
http://www.thebox.myzen.co.uk/Hardware/MIDI_Footsteps.html