Subset of line items through filtered portals

[CoMedia]

I am currently working on a solution for a small restaurant, where the waitresses can enter their orders fast and efficiently. The idea is that they have one main entry screen (layout) where they can easily switch between clients. Food and drinks are divided into categories (Entrees, Main Courses, Desserts, White Wines, Red Wines, etc.) so you get a fast oversight of what has been ordered.

For this purpose, I want to make filtered portals for each category. In fact this is a subset of the line items, filtered per category. So in portal 1 you can enter only the entrees for the client (with a related value list), in portal 2 only the main courses, etcetera. You get the idea, hopefully.

I have tried many ways to accomplish this, but they get far too complex with many special relations for each category. There must be a simpler, more universal, clean and efficient way to get the same, but I am overlook it I guess. Can anyone point me in the right direction?

If you like, you can download a stripped-down version of the solution here.