RE: Group Items and/or Hide Items
I would have to further explore assembly BOMs to fully understand their capabilities. We shied away from using assemblies in QB because of how rigid they were. Perhaps they are more flexible in BC? From my experience, assemblies were best used when the items that made up an assembly would never change in quantity or type. You also couldn't modify components of an assembly from a sales transaction (quote, sales order, etc.). This created all kinds headaches if there was any variation in the quantity or items used from project to project.
Prior to using groups we would add a "master" sales item with the same description and price from the customer's PO, and add the items used below it with $0 resale. Then there was a setting in QB that prevented $0 resale items from printing to invoices. The problem this created for us was that the sales income amounts for each item did not properly report out on the income statement for the project. For example, there was no way for us to separate out income for labor vs. hardware. Groups solved this by allowing us to hide the individual items that made up the group, while still capturing the income per item.
Sorry for the long response!