Hello!
I’d suggest you to try CS-Cart Multi-Vendor if you want to build a big marketplace. Multi-Vendor can handle high load and has lots of ecommerce features in the box. Check this marketplace built on CS-Cart Multi-Vendor—ShopClues. It has insane number of SKUs and vendors.
P.S. If you can’t open ShopClues, try to connect via VPN (it’s closed for some countries).