Great! Glad the memory error is now fixed. WooCommerce *requires* the Permalinks otherwise a lot of stuff will break. And since WC Vendors requires WooCommerce to work, one cant work without the other. ??
If mysite.com/vendors/username/ is showing products from ALL users, then the /username/ part is wrong. The username you enter must be the user_login or the vendors store name. If your’e trying to show YOUR products as the ADMIN they wont be shown there, since ADMINS are NOT VENDORS. If you want the site admin/owners products to show up in a vendor store URL, you need to create an additional user for the admins products with a role of vendor (only vendor, not admin+vendor, only vendor ;)), and change the owner of the products via the product editor to the new vendor account.
The quickest way to test if its working, is to add a new user in WordPress, set a role to Vendor, add a test product, and then go to mysite.com/vendors/username/ — If that doesn’t work, please let me know!
Ben