Need advice on setting up a new project

Question

Hello,
I'm creating a rather complicated project in flash and as3 and would like some advice on how I should set it up.
It requires a login and based on the information the user puts in the login, I need to build a drop down menu.
While logging into the program, the user has to select from one of three categories and one of 10 locations. The main buttons for the drop down are dictated by the categories, each of these buttons have specific modules which will go under each topic. 
example:
category1
category2
category3
category1 uses buttons catA catB catC
category2 uses buttons catA catB
category3 uses buttons catA catC
under cata
module 1
module 2
module 3
module 4
under catb
module 1
module 2
module 3
under catc
module 1
module 2
module 3
module 4
module 5
module 6
module 7
Based on the location the user chooses, a module may have to be added under cata and/or catb and/or catc
The user can click on the buttons in the drop down to skip to different modules, but if they do not it will play in order. Each module has a video, once the video is complete there is an activity/quiz (each of the activities are quite different). Once the activity/quiz is complete, the next module loads until they reach the final module and a lovely final quiz.
Any advice on how to set up a complicated project would be great I've spent a couple of days hunting online and looking at/ trying examples, but all I did was confuse myself.
Warning: I come from an AS2 background... (but not minding as3 so far)

Answer 1

var categoryObj:Object={};
var subcategoryObj:Object={};
subcategoryObj["A"]=["mod1","mod2","mod3","mod4"];
subcategoryObj["B"]=["mod1","mod2","mod3"];
subcategoryObj["C"]=["mod1"];
categoryObj["1"]=["A","B","C"];
categoryObj["2"]=["A","B"];
categoryObj["3"]=["A","C"];
var moduleA:Array = moduleF(numX.toString());
function moduleF(numS:String):Array{
var a:Array = [];
for(var i:uint=0;i<categoryObj[numS].length;i++){
for(var j:uint=0;j<subcategoryObj[categoryObj[numS][i]].length;j++){
a.push(subcategoryObj[categoryObj[numS][i]][j]);
// use the filter method to remove duplicates
return a;