Help with order form that will update an inventory

Hi,

I was hoping someone could help me with creating an order form in excel that would then update the inventory (the main reason for this is to update the inventory rather than actually store any data).

e.g.
Order for Black Collar with the name jamie - when clicking on proceed it would update the inventory minus 1 black strap and letter J, A, M, I, E

The inventory would consists of Collars, Letter and Charms.
This is where i am having real difficulty and can't figure it out as the order could be for different collar style or colors, there are 2 different letter styles (silver and colored) so the order form would need to know what set of letters to update the quantity against...

I have attached the actual excel sheet i was going to use so you can see exactly what i have got so far but it is almost an empty shell at the moment as i got stuck with this order form/updating inventory part.

As you will see when you open the excel sheet, i would like to be able use the 'Order Form' button to process the order that would then minus the QTY against the inventory.

When you click the 'Inventory' button there are 3 sections (Collars, Letters, Charms) this is where i would like the numbers to update from the 'Order Form'

I hope someone is able to help, i know its a lot to ask.

I have put description examples on the order form to try and help you understand what i am trying to achieve.

Regards,
Jamie