With all types of items, including clothing, the Stocks lists will show all items of that type on the map, including clothing worn or carried by visitors and invaders, and stored in cabinets, etc, so using Stocks will not help you out much for this (see Stocks in the wiki for more info).
The minimum you should do to ensure the dwarfs have enough clothing, is to create a set of orders that produce clothing similar to "make 5 trousers when less than 5 trousers are available", because the Work Orders will only count the clothing that is not already in use (worn by people, forbidden, or being hauled, or otherwise owned by someone).
This will ensure there is always some clothing available, even if it is well-used and worn.The maximum you could do is to create a fancy workshop-->stockpile-->magma system that cycles all slightly used clothing into magma and then rely on work orders to create new clothing.
The dwarfs will be happier due to receiving newer clothing, but this will take more work and resources.Read the wiki sections
"Wear" and "Coverage" to answer your questions on coverage and the "Managing Clothing" section to show how some players control clothing in their fort.
Dwarfs probably assign a higher value to preferred materials when making their selection from the available clothing, but it is just as likely another dwarf will take the item first, so you need to make a lot of clothing of that preferred type to ensure a dwarf gets one.