Finished goods should be an asset account; it is just like raw materials in that regard. We have several asset accounts for inventory- Raws, MFG Accessories, Finished Goods, Demos... as many as you need!
You don't need a Sales Order to make a work order. Just scroll through the work order number and DBA will assign a number, or give it your own series of numbers for stock work orders.
The work order process in terms of WIP is determeined by the part number being built and how the class code for that part number is set up. You can build a part whose class totally expenses it, or for an asset, which most A types and F types are, puts it first into WIP while building and then into FG or Accessory asset account when done.
Hope this helps.