WC Vendors Free and WC Vendors Pro can handle unlimited products and unlimited vendors. No problem. We could care less if you have 1 product or one bajillion quadrillion products.
What does matter, is your webhosting setup. Obviously, if you have more than 10,000 vendors, you have staff of at least 10-15 people handling customer service and a huge tech team. You’d be as big as Amazon.com with 10,000 vendors, too.
So, what is this mystical website you are building that you are curious about if a single plugin can handle the equivalent of trillions of dollars of web sales for *your* site? 🙂
As an actual serious answer, it’s all about your server hardware. If you use GoDaddy and you pay them two dollars a month for hosting, you’ll get two dollars worth of a webserver. Pay more host more. But as for the actual software, WordPress, WooCommerce, and WC Vendors, no problem.