Product ID / SKU / Ref. Code

[salouso]

Hi there

I am fairly new to PS (using PS 1.7.5.2)

I have 5k + products that all have a unique SKU (only important to us, not at all for the customer). That SKU is what is used on all images and import files. It is a 5-8 digit number code.
Then each product has a ref code which is the code our customers use to order and identify the product. i.e. all products from a specific manufactuer and category start with the same 3 digits.
So which field would you suggest using for the SKU (right now I used product ID, but since a can`t choose that on creating a new product and also it doesn`t show on the admin or frontend product page, it seems to be no good choice).  And which field for the Ref. Code?
Is there an addon that would allow me to have two individual fields like the "Reference" field?

Thanks for your help

[salouso]

Anyone here that could help me?