Help Fetching Records - Dynamic Picklists

Help Fetching Records - Dynamic Picklists

Let me first say I am a beginner who has searched forums and video tutorials to piece together Deluge.  Just enough to be dangerous!

I own a home staging business, and I am very excited to create a tool built exclusively to my business!

My first challenge is to create a searchable database of inventory items.  I want to be able to easily search for different items, assign them to projects, etc.  

To be able to sort these items (and modify the sorting structure in the future), I have created 3 different Forms to create categories for sorting.  The names are simplified for explanation, but basically:

Form 1) Add Category
Form 2) Add Sub Category
Form 3) Add Sub Sub Category

QUESTION ONE:  I would like to create a dynamic picklist for these 3 fields, so that when I need this data I don't have to add three separate drop down menus (simplifying the visuals and the data entry steps). 

EX: I want to add a new table lamp to my inventory.  

1:  A Lookup Dropdown displays the existing list of Categories (Furniture - Bed & Bath - Lighting, Art, Decor - Throws & Rugs.)

2.  I select the Lighting, Art, & Decor Category, the dropdown clears, and it reloads with the appropriate Sub Categories (Lighting, Art, Decor).  

3. I select Lighting, the dropdown clears, and the Sub-Sub Categories display (Floor Lamps, Table Lamps).

4. I select "Table Lamps," allowing me to properly sort the new table lamp into the "Table Lamps" category.

I have watched a zillion dynamic pick list videos, read a ton of forum posts, and still NO LUCK.  I believe my problem is that the lookup is returning numerical values and the dropdown wants text?  What am I missing? Here is my coding On User Input:

cur_value = input.Category;
clear Category;
sub1 = Sub_Category[ID != 0 && Category == inputCategory];
Category:ui.add(sub1.Sub_Category.getall());


QUESTION TWO: I am creating a Purchase Form to enter purchases off of receipts and categorize them appropriately.  I am using 3 Subforms on the Purchase Form so that I can collect different data for different items purchased.  I know there is ANOTHER coding trick I have to use to include the same dynamic picklist in a Subform.  Still no luck.

EX:  Purchase Form starts with some basic fields to collect an image of the receipt, a date purchased, etc. Then it has several Subforms.  Subform 1 is an Inventory Subform.  I can collect an image of the item purchased, a price, a qty, and then I want to assign the right inventory category - where I want to use the dynamic pick list.

I think I have to use row. instead of input. but all of the directions I've found haven't been helpful.

Please help?