I can create new Items from the exisiting ones, but when I rename them, the construction set informs me that the item is not unique and will not perform the requested action. If I just re-type the ID, a new item is created but I cannot access it... quantity is = to 0

Usually when you make new items, it does this and sets it at zero. What you want to do so you can use it in game, is put it in a barrel, or sumthin like that. So, just take the item, and put it someplace that you will know how to get to quickly, I usually put it in one of the baskets in front of Dralosa Nithryon's Merchant house. Which is in Balmora, the building all by itself from the left of the Silt Strider. So, just make the item, put it in the game, and safe the plugin. And make sure you select Data Files when you put the Morrowind Disc in and select the new plugin you made, usually at the bottom of the list. Let me know if it works.

Also, if you're going to place an item inside a container, make sure to give that container a unique ID. Otherwise all instances of that container will have the item in it.

To be honest I'm not 100% sure what your question is dippy, could you be a little more clear please?