A clothing shop on repeat production will be able to keep demand with around 200 dwarves. If you have 400 dwarves in your fortress you will probably need two clothing shops.
A single farmer workshop on repeat process plants, and maybe two looms should be enough to supply a clothing workshop. Then have a farm on growing pig tails or rope reeds all year round, or as often as you can manage, with a plant stockpile next to your farmer workshop.
You can put all of the clothing production buildings, including related stockpiles, together in the same area or building, as they're all related. If you keep everything close together things can be very efficient. 10 dwarves would probably be enough to cloth a fortress of 200 forever, while also producing infinite valuable trade goods. If you have 400 dwarves, you probably only need 15 dwarves in the entire clothing production chain, since the farming scales up well.
One 10x10 farm, one farmer workshop, two looms, two clothing workshops. To crew that production you probably need five workers, plus five haulers/farmers, and five dwarves sleeping or boozing. And that will keep about 400 dwarves in masterwork and stylish clothing forever.
Dwarves seem to have no problem wearing goblin clothing, so if you're murdering goblins by the siege, goblin clothing will supplement your own produced clothing. Any extras or any worn out clothes just go in bins for buying all metal objects from traders, or to chuck into the magma chute.