Tax advice requested

[mdlbear]

This is the first year I've actually had, you know, stuff to sell. I understand the general concepts, but there are a couple of things I could use advice on from somebody who's done it before:

• Inventory: I'm assuming I'm supposed to value unsold inventory at my cost, i.e. (total production cost)/(number of items).
• Promo copies: Do I value promotional and contributor copies at cost, or retail price? Again I'm assuming cost. (I'm not worried about gifts here: those I'm just treating as sales to myself.)
• Anything else you think I need to know?