SD BOM - Item category group and item category

Dear Sirs,

My question is regarding SD BOM. I have the following process - the company buys two materials from different suppliers and put this components on the stock. Then the Client make a request for the set of the components. Our company does not do any production or merging with these components, just sells them as a kit. Valuation is made at header material level. Also we have no set as itself on our stock, just components.

Could you please advice me which item category group and item category I should use?

Should I use 0002 or ERLA or LUMF item category group? TAC or TAQ item category?

Thank you in advance, Daria.