Newbie Kits/Assemblies/Groups Question...

Having read all of the Help files, as well as all of what's been posted here on the forum, I'm still very confused about the Kit/Assembly/Group issue... Please help me rise from Newbie to Competent User Any help is appreciated!

Here's our scenario:
We sell pendants on various channels; some ship with a chain, some do not. Of those that do come with chains, some come with the chain from the supplier as a single unit with a single unit cost; others do not come pre-packaged with the chain, but are combined at our warehouse (chains are purchased from a different supplier - NetSuite sees none of that). Thus far we have adjusted the cost of the pendants that ship with - but don't come packaged with - chains, to account for the actual cost of the chains. We do not sell the