The subfolders field is limited to 400 characters. Anything beyond that will be truncated.
The subfolder field is for a list of subfolders that will always be put on along with the content of the main folder when you click the "Wear" icon. Since there always needs to be a delay between two folders being put on, the question is also, do you really want to specify that many subfolders?
The "Wear with options" icon (the shirt icon with cog) will load all the subfolders from your inventory automatically. Also, on premium Wardrobe accounts, there is the an icon to load the subfolders from the inventory on the item directly.
So that would be options to use instead of entering them manually if the purpose is only to have them available to put on.