here is the Custom Wearable Feed

http://subeta.net/cw_shop.php

Putting something in your shop is permanent. How you put it in your shop is up to you, so you should already know the answer to your question. When you put your CW into your CW shop, you had the opportunity to determine all those things about your item.

Nope, not set to unlimited. You can put in as many copies as you want. All the sweaters in my CW shop were direct to CS submissions

I think you'd be able to put 20 more into the shop. I can edit the amounts in my shop currently without a problem, I just changed one to 0 and then back to where it was.