Auto Populate Dynamic List Using Data Validation Drop Down

I have been trying to find out if this is even possible, so far I haven't been able to get an answer online...

I am trying to create a running list based on choices made with Data Validation drop down menus in multiple cells. (FYI - Some of these cells also use VLookUp to account for variables, and the list I am trying to create needs to draw from 2 different sets of data.)

Basically, I want to create a detailed cost breakdown of items which I use on a daily basis. Each item has multiple cost factors, some of which need to be purchased and some of which I already have in stock (in stock costs do need to be included).

I created a sheet which details individual line items for the cost factors of each item I use, which separates these costs into the 2 data sets, purchase & in stock; it's important that I have the distinction between the 2 data sets for internal purposes. (I also want to point out that not every item has an in stock component, so I don't know if this would have an affect but felt it pertinent to mention.)

So the idea is, on Monday I can choose the items I will need to use through the Data Validation drop down menus I've created, and the corresponding costing line items will be auto populated onto a third sheet to create an total accumulative breakdown of all costs for the whole week. I understand there will be redundancies, but having this comprehensive detailed list is the objective.

This seemed simple in my head, but as I work through all of the moving parts - I am finding that it is not! Is there any hope for me?! If anyone could offer a hand, I'd be truly appreciative.

I've attached a version of what I have created, so that you can better understand this unintentionally complicated spreadsheet.

Thanks in advance for any help you can provide!!!