Hi,
I think you are worrying for no reason....
You'd start with a main menu for a choice of the 18 categories, with each sub-menu having 20 or so choices as you described. If you are working in 4:3 then you can have (if memory serves) 36 buttons on a menu, as opposed to 18 buttons on a 16:9 menu.
Create your menus in photoshop (you use this, right?), import all your assets - vid clips etc, make you timelines, one category at a time, and link each button to each timeline - you should be able to keep fairly good track of where you are if you break it into chunks like this....
Dominic Osborne
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Director & Head of Visuals
Eight Eyed Sea Bass Ltd
http://www.eighteyedseabass.com
